gpu: Add memory tracing of GPU transfer buffers.
This implements client and service side tracing of transfer buffers
used by the chromium GPU service.
Note that initialization of the TransferBufferManager is moved to
ContextGroup::Initialize as part of this patch as that allows the
dump provider registration logic in TransferBufferManager to be
consistent with BufferManager, TextureManager, etc. without breaking
any tests.
BUG=523336
Review URL: https://codereview.chromium.org/
1304213002
Cr-Commit-Position: refs/heads/master@{#345454}