Fix null pointer exception in WebViewColorOverlay.
Fix null pointer exception in WebViewColorOverlay.

Discovered this while debugging WorkerTest.SharedWorkerHttpAuth for
Bug 106383.

BUG=103386
TEST=None


Review URL: http://codereview.chromium.org/8771055

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@113417 0039d316-1c4b-4281-b951-d872f2087c98

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