Fix a chrome crash seen at times in chrome frame reliability test runs. It appears that the crash occurs because we attempt to unregister focus manager accelerators registered by the external tab container twice as the Uninitialize function gets invoked twice in WM_DESTROY and in the destructor.
Fix a chrome crash seen at times in chrome frame reliability test runs. It appears that the crash occurs because we attempt to
unregister focus manager accelerators registered by the external tab container twice as the Uninitialize function gets invoked
twice in WM_DESTROY and in the destructor.

Fix is to set the focus_manager_ pointer to NULL after unregistering the accelerators.

Bug=42365

Review URL: http://codereview.chromium.org/2069015

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@47958 0039d316-1c4b-4281-b951-d872f2087c98

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