Use gyp_helper in gyp_packager.py

build/gyp_chromium uses gyp_helper to get variables for GYP from
chromium.gyp_env file.
More on chromium.gyp_env can be found here
http://www.chromium.org/developers/how-tos/component-build

This is useful if you want to override some GYP varibles to test
different flags, e.g. using clang to build.

Change-Id: I14fc76abdd6503bf66ef3e27fb9216b3fb8aaa02

gyp_packager.py

@@ -36,12 +36,18 @@ import sys
 
 src_dir = os.path.dirname(os.path.realpath(__file__))
 
+sys.path.insert(0, os.path.join(src_dir, 'build'))
+import gyp_helper
+
 sys.path.insert(0, os.path.join(src_dir, 'tools', 'gyp', 'pylib'))
 import gyp
 
 if __name__ == '__main__':
   args = sys.argv[1:]
 
+  # Allow src/.../chromium.gyp_env to define GYP variables.
+  gyp_helper.apply_chromium_gyp_env()
+
   # If we didn't get a gyp file, then fall back to assuming 'packager.gyp' from
   # the same directory as the script.
   if [arg.endswith('.gyp') for arg in args].count(True) == 0: