Unify PlainTextOffsets and TextIterator's location and length into PlainTextRange

This patch introduces PlainTextRange to unify PlainTextOffsets and TextIterator's location and length, which is used in TextIterator::rangeFromLocationAndLength() and getLocationAndLengthFromRange() for ease of maintenance.

BUG=n/a
TEST=n/a; no behavior changes

Review URL: https://codereview.chromium.org/36813002

git-svn-id: svn://svn.chromium.org/blink/trunk@160503 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Delete make-hash-tools.pl

There's no reason to have a Perl script wrapper around gperf. We can just call
gperf directly from GYP.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/40333005

git-svn-id: svn://svn.chromium.org/blink/trunk@160504 bbb929c8-8fbe-4397-9dbb-9b2b20218538