GitLab

Clamps the character ranges for which bounds are requested so that they fall within the number of pixel offsets provided by Blink.

Blink doesn't always return the location of all the characters in  an inline text box.
BUG=674273
R=dmazzoni@chromium.org
TESTED=manually using NVDA's Python Console and by calling get_characterExtents(offset, 0) and (offset, 1) on a few paragraphs

Review-Url: https://codereview.chromium.org/2579323002
Cr-Commit-Position: refs/heads/master@{#439165}