Inlining more methods into headers.

In total the patch series improves performance by about 60-70% in the
Vulkan draw call overhead test.

Bug: angleproject:2786
Change-Id: I70913ac6b3d5836c17c13e249950987df362f203
Reviewed-on: https://chromium-review.googlesource.com/1194883
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>