UMA histogram for longest renderer main thread usage for page save to MHTML.

UMA histogram for longest renderer main thread usage for page save to MHTML.

The information about the time taken by the main render process thread
for saving a page to MHTML is the main feedback we have to see how much
the operation impacts user experience.

The existing UMA that tracks this information,
PageSerialization.MhtmlGeneration.RendererMainThreadTime.SingleFrame,
is not directly useful for the purpose above because it includes reports
for all frames in a page save operation. For pages with many frames, most
of them are very simple and quickly saved, while one -- generally the
main frame -- is the slowest. So we have a huge amount of low-value
samples pulling the statistics down.

This change adds a new histogram,
PageSerialization.MhtmlGeneration.RendererMainThreadTime.SlowestFrame,
that reports only the longest of all times from the former one in a
single HTML page saving operation, which is the most important one in
terms of user experience.

BUG=645686
Review-Url: https://codereview.chromium.org/2400383002
Cr-Commit-Position: refs/heads/master@{#424312}
(cherry picked from commit 90bf4f0c77709ddb65b1f8d86e04065aacae02ac)

Committed: https://chromium.googlesource.com/chromium/src/+/67c28ff356fd4c8115cefb2ea2fc9bf8510db02c

[carlosk, 2016-10-12 18:08:15]

Description was changed from

==========
UMA histogram for longest renderer main thread usage for page save to MHTML.

The information about the time taken by the main render process thread
for saving a page to MHTML is the main feedback we have to see how much
the operation impacts user experience.

The existing UMA that tracks this information,
PageSerialization.MhtmlGeneration.RendererMainThreadTime.SingleFrame,
is not directly useful for the purpose above because it includes reports
for all frames in a page save operation. For pages with many frames, most
of them are very simple and quickly saved, while one -- generally the
main frame -- is the slowest. So we have a huge amount of low-value
samples pulling the statistics down.

This change adds a new histogram,
PageSerialization.MhtmlGeneration.RendererMainThreadTime.SlowestFrame,
that reports only the longest of all times from the former one in a
single HTML page saving operation, which is the most important one in
terms of user experience.

BUG=645686

Review-Url: https://codereview.chromium.org/2400383002
Cr-Commit-Position: refs/heads/master@{#424312}
(cherry picked from commit 90bf4f0c77709ddb65b1f8d86e04065aacae02ac)
==========

to

==========
UMA histogram for longest renderer main thread usage for page save to MHTML.

The information about the time taken by the main render process thread
for saving a page to MHTML is the main feedback we have to see how much
the operation impacts user experience.

The existing UMA that tracks this information,
PageSerialization.MhtmlGeneration.RendererMainThreadTime.SingleFrame,
is not directly useful for the purpose above because it includes reports
for all frames in a page save operation. For pages with many frames, most
of them are very simple and quickly saved, while one -- generally the
main frame -- is the slowest. So we have a huge amount of low-value
samples pulling the statistics down.

This change adds a new histogram,
PageSerialization.MhtmlGeneration.RendererMainThreadTime.SlowestFrame,
that reports only the longest of all times from the former one in a
single HTML page saving operation, which is the most important one in
terms of user experience.

BUG=645686

Review-Url: https://codereview.chromium.org/2400383002
Cr-Commit-Position: refs/heads/master@{#424312}
(cherry picked from commit 90bf4f0c77709ddb65b1f8d86e04065aacae02ac)

Committed:
https://chromium.googlesource.com/chromium/src/+/67c28ff356fd4c8115cefb2ea2fc...
==========

[carlosk, 2016-10-12 18:08:16]

Committed patchset #1 (id:1) manually as
67c28ff356fd4c8115cefb2ea2fc9bf8510db02c (tree was closed).