Fix memory stomping by ImageLoadingTracker in BrowserActionButton.

In the views code, tracker_ is set to null in this case.  Without
this, I get lots of random crashes when I have 2 page actions
installed (buildbot extension and google tasks extension) and I open
close lots of windows.

BUG=26751,25558

Review URL: http://codereview.chromium.org/379020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@31534 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed