Revert of Touch emulator: overwrite timestamps from mouse event with current time.

Revert of Touch emulator: overwrite timestamps from mouse event with current time. (https://codereview.chromium.org/250923005/)

Reason for revert:
Somewhat speculative; looks like this caused TouchEmulatorTest failures on valgrind:

http://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28tsan%29%283%29/builds/11052

TouchEmulatorTest.Pinch:
../../content/browser/renderer_host/input/touch_emulator_unittest.cc:254: Failure
Value of: ExpectedEvents()
Actual: "TouchEnd GestureFlingStart"
Expected: "TouchEnd GestureScrollEnd"

etc

Original issue's description:
> Touch emulator: overwrite timestamps from mouse event with current time.
> 
> On some platfroms, mouse events come with a bad timestamp, which leads to
> awkward time-dependent gestures. For example, fling animation may be almost
> instant.
> Using base::TimeTicks::Now() is good enough for emulation purposes, because
> emulator spawns new events itself.
> 
> BUG=367156
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266548

TBR=jdduke@chromium.org,dgozman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=367156
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266610

[Nico, 2014-04-28 18:26:37]

Created Revert of Touch emulator: overwrite timestamps from mouse event with
current time.

[commit-bot: I haz the power, 2014-04-28 18:28:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/thakis@chromium.org/252963002/1

[commit-bot: I haz the power, 2014-04-28 18:30:01]

Change committed as 266610