Vertical GlowEffect shown on about:blank page in low end devices

GlowEffect is suppressed when the scrolling is not possible on that particular  
axes. In the about:blank Page horizontal and vertical scrolling is impossible, 
so Horizontal and Vertical Glow effect is not shown in the high end devices. 
But in the low end devices with device_scale_factor = 1.5 
scaled_scroll_bounds in LayerImpl::MaxScrollOffset has decimal fraction 
because of device_scale_factor due to which max_offset is non-zero, which 
fails the below condition in LayerTreeHostImpl::ScrollBy function and this 
triggers the GlowEffect.ToFlooredSize of scaled_scroll_bounds solves the issue.

if (std::abs(active_tree_->TotalMaxScrollOffset().x()) <= kEpsilon)
    unused_root_delta.set_x(0.0f);
if (std::abs(active_tree_->TotalMaxScrollOffset().y()) <= kEpsilon)
    unused_root_delta.set_y(0.0f);

BUG=363527
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=265188

[MuVen, 2014-04-15 08:55:41]

PTAL

[aelias_OOO_until_Jul13, 2014-04-16 22:25:43]

Could you write a test for this?

https://codereview.chromium.org/238753004/diff/1/cc/layers/layer_impl.cc
File cc/layers/layer_impl.cc (right):

https://codereview.chromium.org/238753004/diff/1/cc/layers/layer_impl.cc#newc...
cc/layers/layer_impl.cc:1204: return gfx::ToFlooredVector2d(max_offset);
There's already a floor here that's supposed to fix this, seems it's not working
properly.  I think we should have at most one floor in this function.  Would it
work to move the floor before max_offset.Scale(1 / scale_factor); ?

[MuVen, 2014-04-21 05:35:27]

Added unitest case. PTAL. ToFlooredSize(scaled_scroll_bounds) this solves the
issue. as device scale factor is 1.5 dividing the bounds makes 
scaled_scroll_bounds to [320, 469.877533] and scrol_clip_layer has value 
[320,469]. when we subtract is we are getting a delta of 0.877533 and 
this gets scaled at max_offset.Scale(1 / scale_factor); and makes 
maxscrolloffset to [0,2] which triggers the gloweffect.

[MuVen, 2014-04-21 11:59:21]

I think gfx::ToFlooredVector2d(max_offset) is needed as we are going to scale
the max_offset which is calculated by scaled_scroll_bounds. 
Ple post your views(if im wrong).

[aelias_OOO_until_Jul13, 2014-04-22 02:09:46]

OK, lgtm.

https://codereview.chromium.org/238753004/diff/40001/cc/trees/layer_tree_host...
File cc/trees/layer_tree_host_impl_unittest.cc (right):

https://codereview.chromium.org/238753004/diff/40001/cc/trees/layer_tree_host...
cc/trees/layer_tree_host_impl_unittest.cc:3175: TEST_F(LayerTreeHostImplTest,
NoOverscrollOnLowEndDevice) {
Please rename to "NoOverscrollOnFractionalDeviceScale".

[MuVen, 2014-04-22 03:00:24]

The CQ bit was checked by sataya.m@samsung.com

[commit-bot: I haz the power, 2014-04-22 03:00:52]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sataya.m@samsung.com/238753004/60001

[commit-bot: I haz the power, 2014-04-22 05:53:41]

Change committed as 265188