Fix crash during build/gyp_chromium time.
Fix crash during build/gyp_chromium time.

Without GYP_DEFINES set, build/gyp_chromium would crash with

Generating gyp files from GN...
Traceback (most recent call last):
  File "./build/gyp_chromium", line 207, in <module>
    if not RunGN(supplemental_includes):
  File "./build/gyp_chromium", line 147, in RunGN
    gyp_vars = GetVarsStringForGN(supplemental_includes)
  File "./build/gyp_chromium", line 79, in GetVarsStringForGN
    items = shlex.split(env_string)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shlex.py", line 279, in split
    return list(lex)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shlex.py", line 269, in next
    token = self.get_token()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shlex.py", line 96, in get_token
    raw = self.read_token()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shlex.py", line 124, in read_token
    nextchar = self.instream.read(1)
AttributeError: 'list' object has no attribute 'read'

This was broken by r238475

BUG=321352

Review URL: https://codereview.chromium.org/103253002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@238486 0039d316-1c4b-4281-b951-d872f2087c98

jaruba/chromium.src,krieger-od/nwjs_chromium.src,Chilledheart/chromium,M4sse/chromium.src,krieger-od/nwjs_chromium.src,patrickm/chromium.src,fujunwei/chromium-crosswalk,ondra-novak/chromium.src,Fireblend/chromium-crosswalk,dushu1203/chromium.src,Just-D/chromium-1,markYoungH/chromium.src,Fireblend/chromium-crosswalk,Just-D/chromium-1,TheTypoMaster/chromium-crosswalk,krieger-od/nwjs_chromium.src,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,bright-sparks/chromium-spacewalk,PeterWangIntel/chromium-crosswalk,hgl888/chromium-crosswalk-efl,hgl888/chromium-crosswalk-efl,M4sse/chromium.src,ChromiumWebApps/chromium,krieger-od/nwjs_chromium.src,M4sse/chromium.src,fujunwei/chromium-crosswalk,krieger-od/nwjs_chromium.src,anirudhSK/chromium,Fireblend/chromium-crosswalk,Pluto-tv/chromium-crosswalk,dednal/chromium.src,ChromiumWebApps/chromium,dushu1203/chromium.src,dednal/chromium.src,markYoungH/chromium.src,hgl888/chromium-crosswalk-efl,littlstar/chromium.src,jaruba/chromium.src,TheTypoMaster/chromium-crosswalk,jaruba/chromium.src,bright-sparks/chromium-spacewalk,ondra-novak/chromium.src,PeterWangIntel/chromium-crosswalk,chuan9/chromium-crosswalk,Just-D/chromium-1,Jonekee/chromium.src,krieger-od/nwjs_chromium.src,hgl888/chromium-crosswalk,hgl888/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,Jonekee/chromium.src,jaruba/chromium.src,ltilve/chromium,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk-efl,anirudhSK/chromium,dednal/chromium.src,bright-sparks/chromium-spacewalk,Chilledheart/chromium,hgl888/chromium-crosswalk,markYoungH/chromium.src,ltilve/chromium,M4sse/chromium.src,dednal/chromium.src,dednal/chromium.src,ChromiumWebApps/chromium,axinging/chromium-crosswalk,dushu1203/chromium.src,PeterWangIntel/chromium-crosswalk,markYoungH/chromium.src,chuan9/chromium-crosswalk,axinging/chromium-crosswalk,hgl888/chromium-crosswalk,M4sse/chromium.src,mohamed--abdel-maksoud/chromium.src,hgl888/chromium-crosswalk-efl,crosswalk-project/chromium-crosswalk-efl,dednal/chromium.src,TheTypoMaster/chromium-crosswalk,jaruba/chromium.src,fujunwei/chromium-crosswalk,Jonekee/chromium.src,crosswalk-project/chromium-crosswalk-efl,ltilve/chromium,anirudhSK/chromium,dushu1203/chromium.src,dushu1203/chromium.src,ltilve/chromium,axinging/chromium-crosswalk,hgl888/chromium-crosswalk-efl,ChromiumWebApps/chromium,Chilledheart/chromium,hgl888/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,jaruba/chromium.src,PeterWangIntel/chromium-crosswalk,patrickm/chromium.src,bright-sparks/chromium-spacewalk,mohamed--abdel-maksoud/chromium.src,mohamed--abdel-maksoud/chromium.src,patrickm/chromium.src,Jonekee/chromium.src,anirudhSK/chromium,ltilve/chromium,Pluto-tv/chromium-crosswalk,dednal/chromium.src,ondra-novak/chromium.src,TheTypoMaster/chromium-crosswalk,Pluto-tv/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,bright-sparks/chromium-spacewalk,axinging/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,markYoungH/chromium.src,markYoungH/chromium.src,ondra-novak/chromium.src,littlstar/chromium.src,mohamed--abdel-maksoud/chromium.src,mohamed--abdel-maksoud/chromium.src,dednal/chromium.src,patrickm/chromium.src,ondra-novak/chromium.src,anirudhSK/chromium,markYoungH/chromium.src,TheTypoMaster/chromium-crosswalk,ChromiumWebApps/chromium,mohamed--abdel-maksoud/chromium.src,Just-D/chromium-1,fujunwei/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,Chilledheart/chromium,krieger-od/nwjs_chromium.src,Fireblend/chromium-crosswalk,anirudhSK/chromium,Pluto-tv/chromium-crosswalk,anirudhSK/chromium,hgl888/chromium-crosswalk-efl,ltilve/chromium,M4sse/chromium.src,chuan9/chromium-crosswalk,M4sse/chromium.src,ChromiumWebApps/chromium,axinging/chromium-crosswalk,ltilve/chromium,axinging/chromium-crosswalk,Just-D/chromium-1,ondra-novak/chromium.src,markYoungH/chromium.src,ondra-novak/chromium.src,Pluto-tv/chromium-crosswalk,hgl888/chromium-crosswalk-efl,axinging/chromium-crosswalk,axinging/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,Just-D/chromium-1,Fireblend/chromium-crosswalk,jaruba/chromium.src,crosswalk-project/chromium-crosswalk-efl,hgl888/chromium-crosswalk,PeterWangIntel/chromium-crosswalk,krieger-od/nwjs_chromium.src,patrickm/chromium.src,jaruba/chromium.src,ltilve/chromium,ChromiumWebApps/chromium,chuan9/chromium-crosswalk,M4sse/chromium.src,littlstar/chromium.src,anirudhSK/chromium,patrickm/chromium.src,chuan9/chromium-crosswalk,patrickm/chromium.src,Fireblend/chromium-crosswalk,ltilve/chromium,littlstar/chromium.src,Just-D/chromium-1,ChromiumWebApps/chromium,mohamed--abdel-maksoud/chromium.src,markYoungH/chromium.src,TheTypoMaster/chromium-crosswalk,ondra-novak/chromium.src,Fireblend/chromium-crosswalk,bright-sparks/chromium-spacewalk,Jonekee/chromium.src,hgl888/chromium-crosswalk-efl,chuan9/chromium-crosswalk,littlstar/chromium.src,krieger-od/nwjs_chromium.src,jaruba/chromium.src,fujunwei/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,markYoungH/chromium.src,ondra-novak/chromium.src,bright-sparks/chromium-spacewalk,hgl888/chromium-crosswalk,axinging/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,ChromiumWebApps/chromium,Pluto-tv/chromium-crosswalk,anirudhSK/chromium,Fireblend/chromium-crosswalk,anirudhSK/chromium,axinging/chromium-crosswalk,TheTypoMaster/chromium-crosswalk,jaruba/chromium.src,fujunwei/chromium-crosswalk,chuan9/chromium-crosswalk,dushu1203/chromium.src,krieger-od/nwjs_chromium.src,ChromiumWebApps/chromium,dushu1203/chromium.src,ChromiumWebApps/chromium,Pluto-tv/chromium-crosswalk,mohamed--abdel-maksoud/chromium.src,crosswalk-project/chromium-crosswalk-efl,Chilledheart/chromium,dednal/chromium.src,dushu1203/chromium.src,jaruba/chromium.src,Jonekee/chromium.src,dushu1203/chromium.src,dednal/chromium.src,ChromiumWebApps/chromium,M4sse/chromium.src,krieger-od/nwjs_chromium.src,PeterWangIntel/chromium-crosswalk,dushu1203/chromium.src,Jonekee/chromium.src,M4sse/chromium.src,Jonekee/chromium.src,littlstar/chromium.src,Jonekee/chromium.src,Chilledheart/chromium,littlstar/chromium.src,hgl888/chromium-crosswalk,patrickm/chromium.src,Chilledheart/chromium,mohamed--abdel-maksoud/chromium.src,bright-sparks/chromium-spacewalk,chuan9/chromium-crosswalk,crosswalk-project/chromium-crosswalk-efl,fujunwei/chromium-crosswalk,markYoungH/chromium.src,Jonekee/chromium.src,Fireblend/chromium-crosswalk,anirudhSK/chromium,Just-D/chromium-1,M4sse/chromium.src,crosswalk-project/chromium-crosswalk-efl,dednal/chromium.src,dushu1203/chromium.src,hgl888/chromium-crosswalk,littlstar/chromium.src,bright-sparks/chromium-spacewalk,Just-D/chromium-1,hgl888/chromium-crosswalk-efl,fujunwei/chromium-crosswalk,fujunwei/chromium-crosswalk,Jonekee/chromium.src,patrickm/chromium.src,chuan9/chromium-crosswalk