Add trace event for FirstMeaningfulPaint candidates

Add trace event for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Committed: https://crrev.com/1b6b36c1f28b31bdcf35d207d83e2693b75b5408
Cr-Commit-Position: refs/heads/master@{#414296}

[Kunihiko Sakamoto, 2016-08-24 05:29:04]

Description was changed from

==========
Log trace events for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time
m_provisionalFirstMeaningfulPaint is updated.

The trace-based implementation can find FirstMeaningfulPaint by looking
for the last event in the trace.

BUG=638124
==========

to

==========
Log trace events for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time
m_provisionalFirstMeaningfulPaint is updated.

The trace-based implementation can find FirstMeaningfulPaint by looking
for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Kunihiko Sakamoto, 2016-08-24 05:31:15]

Description was changed from

==========
Log trace events for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time
m_provisionalFirstMeaningfulPaint is updated.

The trace-based implementation can find FirstMeaningfulPaint by looking
for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Log trace events for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Kunihiko Sakamoto, 2016-08-24 05:34:04]

Description was changed from

==========
Log trace events for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Add trace event for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[Kunihiko Sakamoto, 2016-08-24 05:47:25]

ksakamoto@chromium.org changed reviewers:
+ kouhei@chromium.org

[kouhei (in TOK), 2016-08-24 10:45:37]

The change lg, but I'm not sure if this needs to be landed. Would you explain
why you want this landed?

[Kunihiko Sakamoto, 2016-08-25 01:28:13]

On 2016/08/24 10:45:37, kouhei wrote:
> The change lg, but I'm not sure if this needs to be landed. Would you explain
> why you want this landed?

I would like to change the trace-based FMP implementations to use this
trace event, instead of current LayoutAnalyzer/Print events (once the
inconsistency issue is sorted out).

We already have a FMP trace event (blink.user_timing/FirstMeaningfulPaint)
but it's logged only if network activity is settled down. It would be
inconvenient if one has to wait until fully loaded + 2 secs to get TTFMP
in chrome://tracing. Also, some pages never reach network stable, e.g.
pages that use long-polling.

[kouhei (in TOK), 2016-08-25 01:35:49]

Fair enough. lgtm cq

[kouhei (in TOK), 2016-08-25 01:35:53]

The CQ bit was checked by kouhei@chromium.org

[commit-bot: I haz the power, 2016-08-25 01:36:51]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-25 03:44:54]

Description was changed from

==========
Add trace event for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Add trace event for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

[commit-bot: I haz the power, 2016-08-25 03:44:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-25 03:48:30]

Description was changed from

==========
Add trace event for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
==========

to

==========
Add trace event for FirstMeaningfulPaint candidates

This adds a trace event that is logged every time the provisional
FirstMeaningfulPaint timestamp is updated.

Trace-based implementations can find FirstMeaningfulPaint for the page
load by looking for the last event in the trace.

BUG=638124
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Committed: https://crrev.com/1b6b36c1f28b31bdcf35d207d83e2693b75b5408
Cr-Commit-Position: refs/heads/master@{#414296}
==========

[commit-bot: I haz the power, 2016-08-25 03:48:31]

Patchset 1 (id:??) landed as
https://crrev.com/1b6b36c1f28b31bdcf35d207d83e2693b75b5408
Cr-Commit-Position: refs/heads/master@{#414296}