Change createImageBitmap(Blob) to use ImageDecoder instead of ImageSource

At this moment, createImageBitmap(Blob) uses ImageSource for image decoding,
which internally uses DeferredImageDecoder. However, the problem is that
we cannot set the AlphaPremultiplied and the GammaAndColorProfileApplied
parameters in this case.

This CL changes the ImageSource to ImageDecoder where we could explicitly
set the premultiplyAlpha and colorProfile parameters.

This change will makes it easy later on when we handle premultiplyAlpha
=false in the case of createImageBitmap(Blob). Note that this CL
doesn't change any behavior, so as long as all layout tests pass, it
should be fine.

BUG=589132

Review URL: https://codereview.chromium.org/1696753002

Cr-Commit-Position: refs/heads/master@{#378376}
4 files changed