MSE: Add SBRByPts and refactor SBSTest to work for both ByDts and ByPts

Adds SourceBufferRangeByPts implementation (which is currently a
copy of the ByDts implementation) to establish a working baseline of
SBSTests and SBRByPts prior to refactoring SBRByPts to actually do
buffering correctly ByPts.

Rather than using TYPED_TESTs (which would have required most test
case lines to be prefixed by "this->"), TestWithPararam/TEST_P, new
helper macros, and new conditional fixture logic are used to resolve
the correct SourceBufferStream<Range Type> being tested.

BUG=718641
TEST=183 existing LegacyByDts/SourceBufferRangeTests and 183 new NewByPts/SourceBufferRangeTests

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: Ib771f838ba7bbd133ed6d717d27c08c4fcfe4684
Reviewed-on: https://chromium-review.googlesource.com/674529
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503456}
5 files changed