[blink_perf] Add log messages for tracing metrics in blink_perf

[blink_perf] Add log messages for tracing metrics in blink_perf

We add the following log messages:
* Error message when one of tracingCategories & traceEventsToMeasure is specified
but not the other.
* Hint users to use tools/perf/run_benchmark to get tracing based metrics

BUG=701059
Review-Url: https://codereview.chromium.org/2856463003
Cr-Commit-Position: refs/heads/master@{#468332}
Committed: https://chromium.googlesource.com/chromium/src/+/837b0ae2aa5d5755b995951575c3c57ee96f76fe

[nednguyen, 2017-05-01 15:26:59]

nednguyen@google.com changed reviewers:
+ wangxianzhu@chromium.org

[nednguyen, 2017-05-01 15:27:18]

The CQ bit was checked by nednguyen@google.com to run a CQ dry run

[commit-bot: I haz the power, 2017-05-01 15:27:36]

Dry run: CQ is trying da patch.

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

[Xianzhu, 2017-05-01 15:58:54]

lgtm

[nednguyen, 2017-05-01 15:59:09]

The CQ bit was unchecked by nednguyen@google.com

[nednguyen, 2017-05-01 15:59:12]

The CQ bit was checked by nednguyen@google.com

[commit-bot: I haz the power, 2017-05-01 15:59:15]

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, 2017-05-01 16:59:13]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1493654352263630, "parent_rev":
"ca8595ada8cf0a185b7abc5d112c7e9dcd66e3bb", "commit_rev":
"837b0ae2aa5d5755b995951575c3c57ee96f76fe"}

[commit-bot: I haz the power, 2017-05-01 16:59:26]

Description was changed from

==========
[blink_perf] Add log messages for tracing metrics in blink_perf

We add the following log messages:
* Error message when one of tracingCategories & traceEventsToMeasure is
specified
but not the other.
* Hint users to use tools/perf/run_benchmark to get tracing based metrics

BUG=701059
==========

to

==========
[blink_perf] Add log messages for tracing metrics in blink_perf

We add the following log messages:
* Error message when one of tracingCategories & traceEventsToMeasure is
specified
but not the other.
* Hint users to use tools/perf/run_benchmark to get tracing based metrics

BUG=701059

Review-Url: https://codereview.chromium.org/2856463003
Cr-Commit-Position: refs/heads/master@{#468332}
Committed:
https://chromium.googlesource.com/chromium/src/+/837b0ae2aa5d5755b995951575c3...
==========

[commit-bot: I haz the power, 2017-05-01 16:59:28]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/837b0ae2aa5d5755b995951575c3...