Remove DEFINE_STYLE_IMAGE_TYPE_CASTS use from style_fetched_image.h

The primary motivation of this CL is to replace |ToStyleFetchedImage|
with |To<StyleFetchedImage>|.

This CL also ports other dependent files to refer to a new template
function name.

Bug: 891908
Change-Id: Ib09420e38d5fc23a7890103bf72713882b9c5aa6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1532124
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Abhijeet Kandalkar <abhijeet@igalia.com>
Cr-Commit-Position: refs/heads/master@{#642832}
5 files changed