Enable high resolution time for TimeTicks::Now on Windows Canary

Enable high resolution time for TimeTicks::Now on Windows Canary

This should be unnoticeable, except for improved resolution in places such as window.performance.now().

The feature is enabled if the user is running Canary channel or has manually specified the --enable-high-resolution-time flag. This will only work if the CPU has a non-stop TSC and isn't a broken Athlon processor. UMA data show this is a safe combination.

The flag is propagated to renderer processes so that they know to enable it too.

BUG=158234
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=217172

[darin (slow to review), 2013-08-12 18:57:36]

LGTM

https://codereview.chromium.org/16896018/diff/14001/base/time/time.h
File base/time/time.h (right):

https://codereview.chromium.org/16896018/diff/14001/base/time/time.h#newcode580
base/time/time.h:580: // calls to TimeTicksNow() will have the higher resolution
provided by QPC.
nit: TimeTicksNow() -> TimeTicks::Now() ?

https://codereview.chromium.org/16896018/diff/14001/base/time/time.h#newcode582
base/time/time.h:582: static bool MaybeEnableHighResNowEverywhere();
nit: The "Everywhere" suffix could maybe be more precise, or maybe this method
name could just be something like SetNowIsHighResNowIfSupported or
MaybeSetNowIsHighResNow?

https://codereview.chromium.org/16896018/diff/14001/content/app/content_main_...
File content/app/content_main_runner.cc (right):

https://codereview.chromium.org/16896018/diff/14001/content/app/content_main_...
content/app/content_main_runner.cc:675:
base::TimeTicks::MaybeEnableHighResNowEverywhere();
nit: I think it is more canonical in this file to leave off the {}'s when not
needed.

[James Simonsen, 2013-08-12 22:57:06]

https://codereview.chromium.org/16896018/diff/14001/base/time/time.h
File base/time/time.h (right):

https://codereview.chromium.org/16896018/diff/14001/base/time/time.h#newcode580
base/time/time.h:580: // calls to TimeTicksNow() will have the higher resolution
provided by QPC.
On 2013/08/12 18:57:36, darin wrote:
> nit: TimeTicksNow() -> TimeTicks::Now() ?

Done.

https://codereview.chromium.org/16896018/diff/14001/base/time/time.h#newcode582
base/time/time.h:582: static bool MaybeEnableHighResNowEverywhere();
On 2013/08/12 18:57:36, darin wrote:
> nit: The "Everywhere" suffix could maybe be more precise, or maybe this method
> name could just be something like SetNowIsHighResNowIfSupported or
> MaybeSetNowIsHighResNow?

Done.

https://codereview.chromium.org/16896018/diff/14001/content/app/content_main_...
File content/app/content_main_runner.cc (right):

https://codereview.chromium.org/16896018/diff/14001/content/app/content_main_...
content/app/content_main_runner.cc:675:
base::TimeTicks::MaybeEnableHighResNowEverywhere();
On 2013/08/12 18:57:36, darin wrote:
> nit: I think it is more canonical in this file to leave off the {}'s when not
> needed.

Done.

[commit-bot: I haz the power, 2013-08-12 23:00:29]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/simonjam@chromium.org/16896018/28001

[commit-bot: I haz the power, 2013-08-13 02:46:03]

Change committed as 217172