Automated g4 rollback

*** Reason for rollback ***

i think some of these changes were wrong

*** Original change description ***

Small update to chrome extensions extern
Contributed by amattie
Fixes issue 876
https://code.google.com/p/closure-compiler/issues/detail?id=876

DELTA=22 (1 added, 11 deleted, 10 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=6057


git-svn-id: http://closure-compiler.googlecode.com/svn/trunk@2433 b0f006be-c8cd-11de-a2e8-8d36a3108c74