[Telemetry] Fix --cold-load-percent.

[Telemetry] Fix --cold-load-percent.

Previously, we didn't properly clear all the network caches.
1. DNS and predictor caches were left in tact. This was fixed by calling the
   net benchmarking extension methods.
2. Live resources in the memory cache were left in tact. This is fixed by
   navigating to about:blank to destroy the old renderer.

Also, --enable-net-benchmarking is supported on the stable channel, so we can
remove the workaround.

With this, cold loads are consistent on Android:

*RESULT cold_times: page_load_time= [4637,4493,4479,4564,4611,4549] ms
Avg cold_times: 4555.500000ms
Sd  cold_times: 62.602716ms
RESULT warm_times_by_url: http___www.youtube.com_watch?v_LIJOhk6FscY= [2122,2104,2079,2094] ms
Avg warm_times_by_url: 2099.750000ms
Sd  warm_times_by_url: 18.043928ms

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251252

[shatch, 2014-02-13 23:44:25]

On 2014/02/13 23:27:28, tonyg wrote:

Awesome! Patched it in here, getting much "colder" cold times, non-owner lgtm

[tonyg, 2014-02-13 23:44:50]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-02-13 23:46:20]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tonyg@chromium.org/165193002/1

[slamm, 2014-02-14 00:15:33]

https://codereview.chromium.org/165193002/diff/1/tools/telemetry/telemetry/co...
File tools/telemetry/telemetry/core/tab.py (right):

https://codereview.chromium.org/165193002/diff/1/tools/telemetry/telemetry/co...
tools/telemetry/telemetry/core/tab.py:273: self.Navigate('about:blank')
Does this need to be before the clearCache call?

[tonyg, 2014-02-14 00:19:23]

On 2014/02/14 00:15:33, slamm wrote:
>
https://codereview.chromium.org/165193002/diff/1/tools/telemetry/telemetry/co...
> File tools/telemetry/telemetry/core/tab.py (right):
> 
>
https://codereview.chromium.org/165193002/diff/1/tools/telemetry/telemetry/co...
> tools/telemetry/telemetry/core/tab.py:273: self.Navigate('about:blank')
> Does this need to be before the clearCache call?

It doesn't really matter.

[commit-bot: I haz the power, 2014-02-14 01:31:00]

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

[commit-bot: I haz the power, 2014-02-14 01:31:04]

Retried try job too often on linux_rel for step(s) telemetry_perf_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[tonyg, 2014-02-14 01:45:39]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-02-14 01:46:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tonyg@chromium.org/165193002/150002

[commit-bot: I haz the power, 2014-02-14 04:06:08]

Change committed as 251252