Add a use counter and histogram to FileReaderSync.

Add a use counter and histogram to FileReaderSync.

To hopefully eventually facilitate removing FileReaderSync from service
workers this adds both a use counter and histogram to log how often the
API is used in the various worker types.

BUG=688586
Review-Url: https://codereview.chromium.org/2682223006
Cr-Commit-Position: refs/heads/master@{#449833}
(cherry picked from commit 77f740e334ba6fdb4d6493372e8009c544939ed4)

Review-Url: https://codereview.chromium.org/2694093002 .
Cr-Commit-Position: refs/branch-heads/2987@{#489}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed: https://chromium.googlesource.com/chromium/src/+/f9a5a3f987c9c5c4af122effef4440d97838e568

[Marijn Kruisselbrink, 2017-02-13 21:57:57]

Description was changed from

==========
Add a use counter and histogram to FileReaderSync.

To hopefully eventually facilitate removing FileReaderSync from service
workers this adds both a use counter and histogram to log how often the
API is used in the various worker types.

BUG=688586

Review-Url: https://codereview.chromium.org/2682223006
Cr-Commit-Position: refs/heads/master@{#449833}
(cherry picked from commit 77f740e334ba6fdb4d6493372e8009c544939ed4)
==========

to

==========
Add a use counter and histogram to FileReaderSync.

To hopefully eventually facilitate removing FileReaderSync from service
workers this adds both a use counter and histogram to log how often the
API is used in the various worker types.

BUG=688586

Review-Url: https://codereview.chromium.org/2682223006
Cr-Commit-Position: refs/heads/master@{#449833}
(cherry picked from commit 77f740e334ba6fdb4d6493372e8009c544939ed4)

Review-Url: https://codereview.chromium.org/2694093002 .
Cr-Commit-Position: refs/branch-heads/2987@{#489}
Cr-Branched-From:
ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed:
https://chromium.googlesource.com/chromium/src/+/f9a5a3f987c9c5c4af122effef44...
==========

[Marijn Kruisselbrink, 2017-02-13 21:57:59]

Committed patchset #1 (id:1) manually as
f9a5a3f987c9c5c4af122effef4440d97838e568.