canvas: homogeneise style and simplify methods logic.

This CL homogeneises the if-else bracketing style in said file: these
blocks get {} if either the condition or the body in either branch is
> 1 line.  Otherwise, no brackets.

Simplified the logic of a few service methods too, and extracted
the calculation of CanvasResourceProvider::ResourceUsage |usage|
in GetOrCreateCanvasResourceProvider() so that it looks similar\
on both sides of the branch.

No new functionality intended.

Bug: 839970
Change-Id: I6e275a330f145aea861ae9344aa172ffc5840a27
Reviewed-on: https://chromium-review.googlesource.com/1150437
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578135}
2 files changed