Changed the app list string matching formula.

Changed the app list string matching formula.

This is used to rank apps and webstore results. This should not (really)
affect the relative ranking of any results, only the absolute scores
that they are assigned internally. However, this will be relevant in the
future when we start comparing scores of different types of results
against each other.

The algorithm (used to score app and webstore results) now has a
different tapering formula, designed to reach a higher score with fewer
keystrokes. Previously, it was based on the percentage of the full title
you had typed (which unfairly de-prioritized apps with long titles, such
as "Google Keep - notes and lists"). Now, it has an exponential curve,
so you get a reasonably high score with just a few letters matched, and
then it tapers off, approaching 1.0 as you type more letters.

BUG=422610
Committed: https://crrev.com/4eb24b29619de77aa235ed772135afa391a23797
Cr-Commit-Position: refs/heads/master@{#329574}

[Matt Giuca, 2015-05-12 08:39:46]

mgiuca@chromium.org changed reviewers:
+ calamity@chromium.org

[Matt Giuca, 2015-05-12 08:39:47]

Split off from https://codereview.chromium.org/1113483002/.

This should not affect the results directly (since they are still stratified),
so it makes sense to land this sooner (and we don't have to wait for stats).

[calamity, 2015-05-13 01:19:23]

lgtm

[Matt Giuca, 2015-05-13 02:07:08]

The CQ bit was checked by mgiuca@chromium.org

[commit-bot: I haz the power, 2015-05-13 02:07:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1138193002/1

[commit-bot: I haz the power, 2015-05-13 02:56:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-13 02:57:46]

Patchset 1 (id:??) landed as
https://crrev.com/4eb24b29619de77aa235ed772135afa391a23797
Cr-Commit-Position: refs/heads/master@{#329574}