Implemented ITextRangeProvider::CompareEndpoints

Implemented CompareEndpoints of ITextRangeProvider with assoicated
unittests.

Bug: 928948
Change-Id: I184554c8493e131c05787ef262edf6d0298f9de5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1516879
Commit-Queue: Victor Fei <vicfei@microsoft.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641402}
3 files changed