Revert of https://codereview.chromium.org/104333002/
Reason for revert: Hopefully cl 100393008 should improve things on Windows

Review URL: https://codereview.chromium.org/104653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240112 0039d316-1c4b-4281-b951-d872f2087c98
aw: Allow gyp_webview to be run anywhere

Currently gyp_webview sources chromium envsetup.sh from current
directory, which means it must be run from chromium src. But we already
export this as CHROME_SRC, so use that as prefix.

BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/112243003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240113 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240112
SVN changes up to revision 240113