Fix a browser crash when an extension with multiple active pages crashes.
Fix a browser crash when an extension with multiple active pages crashes.

BUG=63038
TEST=Install an extension with a bg page and a popup. Right-click the browser action and inspect the popup. In the task manager, kill the extension process. The browser should not crash.

Review URL: http://codereview.chromium.org/5038004

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@66342 0039d316-1c4b-4281-b951-d872f2087c98

gavinp/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,ropik/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,Crystalnix/house-of-life-chromium,adobe/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,ropik/chromium,adobe/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,ropik/chromium