support CC/CXX_wrapper in chromium.gyp_env

See https://codereview.chromium.org/13950005/ for where it's required.

R=thakis@chromium.org
BUG=232421

Review URL: https://codereview.chromium.org/14093007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194679 0039d316-1c4b-4281-b951-d872f2087c98

build/gyp_helper.py

@@ -24,9 +24,11 @@ def apply_gyp_environment_from_file(file_path):
     raise
   supported_vars = (
       'CC',
+      'CC_wrapper',
       'CHROMIUM_GYP_FILE',
       'CHROMIUM_GYP_SYNTAX_CHECK',
       'CXX',
+      'CXX_wrapper',
       'GYP_DEFINES',
       'GYP_GENERATOR_FLAGS',
       'GYP_GENERATOR_OUTPUT',