Revert "linux: turn on -Wextra"

Compiled locally and on trybots but failed on builder?!

This reverts commit r42688.

git-svn-id: http://src.chromium.org/svn/trunk/src/build@42689 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -704,7 +704,8 @@
           '-pthread',
           '-fno-exceptions',
           '-Wall',
-          '-Wextra',
+          # TODO(evan): turn this back on once the v8 change lands.
+          #'-Wextra',
           # Don't warn about unused function params.  We use those everywhere.
           '-Wno-unused-parameter',
           # Don't warn about the "struct foo f = {0};" initialization pattern.