cc: Make tiling interest rect calc based on viewport.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 34a75992387791b792b27b79e6573d622bd80461..b236ba662ee8f3b097c96d1aa4e0bda3d63e0569 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -1156,7 +1156,7 @@ scoped_ptr<PictureLayerTilingSet>
 PictureLayerImpl::CreatePictureLayerTilingSet() {
   const LayerTreeSettings& settings = layer_tree_impl()->settings();
   return PictureLayerTilingSet::Create(
-      this, settings.max_tiles_for_interest_area,
+      this, 4 * layer_tree_impl()->device_viewport_size().GetArea(),

[sohanjg, 2015/05/05 12:59:20]

instead of sending viewport area/tile area and then multiplying the same tile
area in PLT::ComputeTilePriorityRects, i am just sending the viewport area in
all 4 directions. will that be ok ?

actually we dont have tile size info here anyways till we create tiling and
decide the content bounds.

[vmpstr, 2015/05/05 20:48:11]

Having a viewport distance in all directions would be 9 * viewport area, right?
(three viewports across three viewports down). Although I think in majority of
cases, there's no wiggle room for left and right. In either case, I think we
should send down here a multiplier (tiling_interest_area_viewport_multiplier or
something), since the viewport size can change without us creating a new tiling
set.

That is, we should use the multiplier in conjunction with the visible rect (that
we get in update tile priorities / compute tile priority rects), and figure out
what the new live tiles rect should be.

[sohanjg, 2015/05/06 15:01:59]

Yeah right (* 9) , i somehow forgot its an area.
Maybe we can check for mobile viewport meta tag and reduce the multiplier (* 3)
in future, i'll leave a todo, if thats ok?

       layer_tree_impl()->use_gpu_rasterization()
           ? settings.gpu_rasterization_skewport_target_time_in_seconds
           : settings.skewport_target_time_in_seconds,