Refactor CanvasResourceProvider::WillDraw()

As part of the effort of introducing scoped SyncToken access in
CanvasResourceProvider, this CL:

1. removes WillDraw() from the CanvasResourceProvider base class;
2. renames CanvasResourceProviderSharedImage::WillDraw() into
   WillDrawUnaccelerated() as this function is only called in the
   unaccelerated case.
3. removes CanvasResourceProvider::WillDraw() from its only callsite in
   EnsureSkiaCanvas(), and instead calls WillDrawUnaccelerated() from
   CanvasResourceProviderSharedImage::WritePixels()/RasterRecord()
   directly.

Bug: 40286368
Change-Id: Ief304e931640b98b059b2b821fd4b2f73faf1712
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7004434
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Mingjing Zhang <mjzhang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1524520}