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Fix the GC of workers. When Worker object is GC'ed in the renderer, we need to terminate the worker process.
BUG=15647, 15759
TEST=new ui_test is part of this CL
Review URL: http://codereview.chromium.org/151125

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@20034 0039d316-1c4b-4281-b951-d872f2087c98