Fix check for b_dir and add depot_tools to PATH
Fix check for b_dir and add depot_tools to PATH

R=sheyang@chromium.org
BUG=498256

Review URL: https://codereview.chromium.org/1317953002 .

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@296442 0039d316-1c4b-4281-b951-d872f2087c98

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