Implement range matching for TextUrlFragments

Implement range matching in TextFragmentFinder. The parsing of the
endText string is already implemented. TextFragmentFinder now
checks if the end text is present in the TextFragmentSelector,
searches for the first occurrence after it finds the start text,
and returns the total range.

Bug: 924964
Change-Id: Ifa913d1aef8d3406c1133608842c5a7d710f9f14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573814
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Nick Burris <nburris@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654134}
4 files changed