Chrome extension extern fixes and cleanup.

R=ewa
DELTA=128 (101 added, 0 deleted, 27 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=6160


git-svn-id: http://closure-compiler.googlecode.com/svn/trunk@2475 b0f006be-c8cd-11de-a2e8-8d36a3108c74