[Blink] Display images on a dark background

Images displayed in a standalone main frame are now displayed
on a color that is almost, but not quite, entirely unlike black.
More specifically, all images will now be displayed on a #0E0E0E
page background, while transparent images are displayed on a
checkerboard image background.

Intent to implement:
https://docs.google.com/document/d/1wJPz4kn-9mEFs_ZEM0hAwwr-YzBdW-5hdX1-jkt81Ng/edit?usp=sharing

BUG=650455

Review-Url: https://codereview.chromium.org/2445413003
Cr-Commit-Position: refs/heads/master@{#429820}
8 files changed