Add some NULL-checks for ExtensionHost::extension to fix a crash bug.

BUG=131401
TEST=no

Review URL: https://chromiumcodereview.appspot.com/10538041

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@141090 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed