Use layout units in PinchViewport::scrollIntoView.

Use layout units in PinchViewport::scrollIntoView.

The pinch viewport visibleRect is snapped to LayoutRect in
RenderBox::scrollRectToVisible, but it remained at full precision
FloatRect when used in PinchViewport::scrollIntoView.  This caused a
small scroll in cases that should've been a no-op.

This changes PinchViewport::scrollIntoView to cast
visibleRect() to a LayoutRect before using it, fixing the issue by
making the imprecision cancel out.  I also changed the argument rect to
a LayoutRect to avoid the reverse problem of too much precision in that
one in the future.

NOTRY=true
BUG=428826
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184818

[aelias_OOO_until_Jul13, 2014-11-01 03:00:14]

aelias@chromium.org changed reviewers:
+ bokan@chromium.org, rbyers@chromium.org

[aelias_OOO_until_Jul13, 2014-11-01 03:00:15]

PTAL, rbyers@ for OWNERS.

Note the unit test I modified had been disabled by the big Harfbuzz patch for
some reason.  It seems to work fine though.

[bokan, 2014-11-03 14:35:47]

lgtm.

FYI, the DISABLED tests were causing problems on some Mac bots sometimes. Turns
out that if a mouse is plugged in (and depending what kind of mouse), the
scrollbar theme changes causing some of these tests to bust (that was a
frustrating day of debugging). I've recently changed these tests to use
MockScrollbars so I'll submit a CL shortly to reenable them all.

[aelias_OOO_until_Jul13, 2014-11-03 19:08:12]

OK, still need Source/core OWNERS from rbyers.

[Rick Byers, 2014-11-04 05:47:16]

LGTM - sorry for the delay, travelling

[aelias_OOO_until_Jul13, 2014-11-04 05:49:06]

The CQ bit was checked by aelias@chromium.org

[commit-bot: I haz the power, 2014-11-04 05:49:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/678153003/1

[commit-bot: I haz the power, 2014-11-04 05:50:34]

Committed patchset #1 (id:1) as 184818