Add ImageResource update bitmap images api

The frames of bitmap images can change due to extrinsic reasons, other than new
network data arrival or image frame animations. Add a new ImageResoruce api for
updating images for extrinsic reasons, with optional decoder reset support used
to force image re-decoding if needed.

TEST=webkit_unit_tests --gtest_filter="ImageResource*UpdateBitmapImages"
BUG=410135, 369901

Review URL: https://codereview.chromium.org/526153002

git-svn-id: svn://svn.chromium.org/blink/trunk@181451 bbb929c8-8fbe-4397-9dbb-9b2b20218538