This simplifies the API from the calling resource classes. This method
is called internally instead. beginWriteResource and
appendWriteResource both call updateSerial internally.

Additionally this removes hasStartedRenderPass and instead returns a
boolean from appendToStartedRenderPass indicating success.

Bug: angleproject:2539
Change-Id: Idcf72e6a80dde90e83dabc64644051bb536c6b12
Reviewed-on: https://chromium-review.googlesource.com/1066554Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>