Delete http_proxy from environment variables if it exists.
Delete http_proxy from environment variables if it exists.

BUG=139638
TBR=nsylvain@chromium.org


Review URL: https://chromiumcodereview.appspot.com/10830070

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@148978 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build