Fix for an annoying ASSERT in blink when we tap on an editable portiion of the page

Fix for an annoying ASSERT in blink when we tap on an editable portiion of the page

The reason for the ASSERT is blink is checking for the force field in the
WebTouchEvent structure to be a valid value between 0 and 1. The touch
event constructor we use in HWNDMessageHandler always ends up setting the
force member in the PointerDetails structure to NaN.

Fix is to use a different flavor of the TouchEvent constructor to set a
force value of 0

BUG=none

[ananta, 2016-07-26 23:42:29]

ananta@chromium.org changed reviewers:
+ sky@chromium.org

[sky, 2016-07-26 23:53:10]

NaN has a useful meaning for PointerDetails:

  // Force (pressure) of the touch. Normalized to be [0, 1] except NaN means
  // pressure is not supported by the input device.

I don't think we should change HWNDMessageHandler. If blink wants to ignore
no-force, it should be updated.