NULL out pending_requests_ when GPU channel fails to be created.

Otherwise the next attempt to create a GPU channel won't create a new pending request and will hang forever.

BUG=365904

Review URL: https://codereview.chromium.org/284003002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@270594 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed