Re-add common.gypi to help fix closure_compilation.

build/gyp_chromium.py

Index: build/gyp_chromium.py
diff --git a/build/gyp_chromium.py b/build/gyp_chromium.py
index 1572762a2658d6dc72539697771c041ae2fdd6be..53bb27a3a79e3110f7221f5c519b7cf9e9308deb 100644
--- a/build/gyp_chromium.py
+++ b/build/gyp_chromium.py
@@ -181,6 +181,9 @@ def additional_include_files(supplemental_files, args=[]):
   if os.environ.get('GYP_INCLUDE_FIRST') != None:
     AddInclude(os.path.join(chrome_src, os.environ.get('GYP_INCLUDE_FIRST')))
 
+  # Always include common.gypi.
+  AddInclude(os.path.join(script_dir, 'common.gypi'))
+
   # Optionally add supplemental .gypi files if present.
   for supplement in supplemental_files:
     AddInclude(supplement)