MSE: Template-ize SourceBufferStream with SourceBufferRange parameter

Makes SourceBufferStream's choice of SourceBufferRange subclass be a
template parameter "RangeClass". This will allow swap-in usage of a new
kind of SourceBufferRange (SourceBufferRangeByPts) in future CLs based
on which kind of SourceBufferStream is constructed, along with custom
SourceBufferStream logic for a subset of its methods where necessary
based on RangeClass choice.

For now, hardcodes construction in test and product to only test
SourceBufferRangeByDts. Includes preparation for refactoring
SourceBufferStreamTests to be TYPED_TESTs. Follow-up CLs will add
...ByPts variant.

BUG=718641

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Ic159c632c58e58b33db2606676884a4ca3afecef
Reviewed-on: https://chromium-review.googlesource.com/673853
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503346}
5 files changed