Code:  static sk_sp<SkImage> unPremulSkImageToPremul(SkImage* input) {
  SkImageInfo info = SkImageInfo::Make(input->width(), input->height(),
                                       kN32_SkColorType, kPremul_SkAlphaType);
  RefPtr<Uint8Array> dstPixels = copySkImageData(input, info);
  if (!dstPixels)
     return nullptr;
   return newSkImageFromRaster(
       info, std::move(dstPixels),
      static_cast<size_t>(input->width()) * info.bytesPerPixel());
 }

Vulnerability Type: 
CWE ID: CWE-787
Summary: Bad casting in bitmap manipulation in Blink in Google Chrome prior to 55.0.2883.75 for Mac, Windows and Linux, and 55.0.2883.84 for Android allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
Commit Message: Prevent bad casting in ImageBitmap when calling ArrayBuffer::createOrNull

Currently when ImageBitmap's constructor is invoked, we check whether
dstSize will overflow size_t or not. The problem comes when we call
ArrayBuffer::createOrNull some times in the code.

Both parameters of ArrayBuffer::createOrNull are unsigned. In ImageBitmap
when we call this method, the first parameter is usually width * height.
This could overflow unsigned even if it has been checked safe with size_t,
the reason is that unsigned is a 32-bit value on 64-bit systems, while
size_t is a 64-bit value.

This CL makes a change such that we check whether the dstSize will overflow
unsigned or not. In this case, we can guarantee that createOrNull will not have
any crash.

BUG=664139

Review-Url: https://codereview.chromium.org/2500493002
Cr-Commit-Position: refs/heads/master@{#431936}