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This cl adds a penalty factor to SequenceMatcher so that
we can penalize lots of short matching blocks.

This cl also update search parameters.

Bug: 1081584,1090181,1090154,1090148
Change-Id: Idd35ddd7cfbcdb3928e4b966f2ec757d0b75296c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2227721
Commit-Queue: Jia Meng <jiameng@chromium.org>
Reviewed-by: Thanh Nguyen <thanhdng@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774930}