Fix integer over flow issue in HTMLCanvasElement::canCreateImageBuffer

Right now in this method, it does a size.width() * size.height(), and
that could cause integer overflow.

This CL fix that by using CheckedNumeric<int>.

BUG=630024

Review-Url: https://codereview.chromium.org/2170693003
Cr-Commit-Position: refs/heads/master@{#406914}
1 file changed