Fix a crash in HungRendererView. |tab_contents_| can be set to NULL when TabContents is destroyed, when RenderViewIsGone and when the tab becomes responsive again. If we happen to press the button just after this happens, we'll get a crash.
Fix a crash in HungRendererView. |tab_contents_| can be set to NULL when TabContents is destroyed, when RenderViewIsGone and when the tab becomes responsive again. If we happen to press the button just after this happens, we'll get a crash.

BUG=http://crbug.com/52293
TEST=None

Review URL: http://codereview.chromium.org/3165022

git-svn-id: http://src.chromium.org/svn/trunk/src@56419 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 8aa672ca36eb78ea6bc914060e9cb45ec9749431
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser