Fix for crash in HTMLCanvasElement::createImageBufferInternal
Fix for crash in HTMLCanvasElement::createImageBufferInternal

This is a rare crash that occurs when a GPU-accelerated
surface becomes invalid shortly after creation. The fix consists in
verifying that ImageBuffer::create returned non-null before using the new
image buffer. The check for a valid image buffer surface was removed
because it is redundant with a check that is done in ImageBuffer::create

BUG=448188

Review URL: https://codereview.chromium.org/898683002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@189458 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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