Fix some issues with the GPU Tracer.

Fix some issues with the GPU Tracer.

I had thought the trace ID for async markers were no longer relevant
since I was using the trace source channel as the ID, but sometimes
they overlap because of timing variances and mess up the traces.
I've made each marker have it's own unique ID once again.

R=vmiura@chromium.org
BUG=478923
Committed: https://crrev.com/151b6d69a92ec2abbe34a6992093a2ca4e597b3e
Cr-Commit-Position: refs/heads/master@{#329155}

[David Yen, 2015-05-08 23:57:00]

dyen@chromium.org changed reviewers:
+ piman@chromium.org

[David Yen, 2015-05-08 23:57:00]

+piman to review ui/gl/gpu_timing.cc

[David Yen, 2015-05-09 00:00:31]

dyen@chromium.org changed reviewers:
- piman@chromium.org

[David Yen, 2015-05-09 00:01:19]

On 2015/05/08 23:57:00, David Yen wrote:
> +piman to review ui/gl/gpu_timing.cc

-piman, decided to add glFlush in a later patch so we can monitor the perf bots
to see if the flush adds significant overhead.

Removed the glFlush() from the CL Description, adding it here to document what
was here:

The timings offset calculations are also off sometimes, they need to
be queried between the first and second timer query. Since we
never flush occasionally we will query the timing offset before the
first query has been flushed. By issuing a flush before we calculate
the timing offset, this will guarantee the first timer query has
been flushed.

[vmiura, 2015-05-09 00:05:52]

The CQ bit was checked by vmiura@chromium.org

[vmiura, 2015-05-09 00:05:53]

lgtm

[commit-bot: I haz the power, 2015-05-09 00:16:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1138603002/20001

[commit-bot: I haz the power, 2015-05-09 04:17:32]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-09 04:17:34]

Try jobs failed on following builders:
  android_chromium_gn_compile_dbg on tryserver.chromium.linux (JOB_TIMED_OUT, no
build URL)
  android_chromium_gn_compile_rel on tryserver.chromium.linux (JOB_TIMED_OUT, no
build URL)
  cast_shell_android on tryserver.chromium.linux (JOB_TIMED_OUT, no build URL)
  cast_shell_linux on tryserver.chromium.linux (JOB_TIMED_OUT, no build URL)
  linux_chromium_asan_rel_ng on tryserver.chromium.linux (JOB_TIMED_OUT, no
build URL)
  linux_chromium_chromeos_compile_dbg_ng on tryserver.chromium.linux
(JOB_TIMED_OUT, no build URL)
  linux_chromium_chromeos_ozone_rel_ng on tryserver.chromium.linux
(JOB_TIMED_OUT, no build URL)
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_TIMED_OUT, no
build URL)
  linux_chromium_clobber_rel_ng on tryserver.chromium.linux (JOB_TIMED_OUT, no
build URL)
  linux_chromium_gn_chromeos_rel on tryserver.chromium.linux (JOB_TIMED_OUT, no
build URL)
  linux_chromium_gn_dbg on tryserver.chromium.linux (JOB_TIMED_OUT, no build
URL)
  linux_chromium_gn_rel on tryserver.chromium.linux (JOB_TIMED_OUT, no build
URL)
  linux_chromium_rel_ng on tryserver.chromium.linux (JOB_TIMED_OUT, no build
URL)
  mac_chromium_compile_dbg_ng on tryserver.chromium.mac (JOB_TIMED_OUT, no build
URL)
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_TIMED_OUT, no build URL)
  win_chromium_compile_dbg_ng on tryserver.chromium.win (JOB_TIMED_OUT, no build
URL)
  win_chromium_rel_ng on tryserver.chromium.win (JOB_TIMED_OUT, no build URL)
  win_chromium_x64_rel_ng on tryserver.chromium.win (JOB_TIMED_OUT, no build
URL)

[David Yen, 2015-05-11 15:22:35]

The CQ bit was checked by dyen@chromium.org

[commit-bot: I haz the power, 2015-05-11 15:22:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1138603002/20001

[commit-bot: I haz the power, 2015-05-11 16:30:37]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-11 16:32:02]

Patchset 2 (id:??) landed as
https://crrev.com/151b6d69a92ec2abbe34a6992093a2ca4e597b3e
Cr-Commit-Position: refs/heads/master@{#329155}