cc: Restore the space of interest area padding to be ideal contents s…

…pace.

This patch ensures that the interest area padding we use is specified in
ideal contents scale, not in screen scale. Effectively this means that
on devices with content scale > 1, we will have a smaller interest area.

This restores the behavior that was changed when the calculation was
moved to the tiling set.

R=ericrk, enne
BUG=614990
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2022613002
Cr-Commit-Position: refs/heads/master@{#396602}

cc/tiles/picture_layer_tiling_set.cc

@@ -474,8 +474,9 @@ void PictureLayerTilingSet::UpdatePriorityRects(
   // We keep things as floats in here.
   if (!visible_rect_in_layer_space.IsEmpty()) {
     gfx::RectF eventually_rectf(visible_rect_in_layer_space);
-    eventually_rectf.Inset(-tiling_interest_area_padding_,
-                           -tiling_interest_area_padding_);
+    eventually_rectf.Inset(
+        -tiling_interest_area_padding_ / ideal_contents_scale,
+        -tiling_interest_area_padding_ / ideal_contents_scale);
     if (eventually_rectf.Intersects(
             gfx::RectF(gfx::SizeF(raster_source_->GetSize())))) {
       visible_rect_in_layer_space_ = visible_rect_in_layer_space;

cc/trees/layer_tree_settings.cc

@@ -85,6 +85,9 @@ LayerTreeSettings::LayerTreeSettings()
       max_untiled_layer_size(gfx::Size(512, 512)),
       minimum_occlusion_tracking_size(gfx::Size(160, 160)),
       // 3000 pixels should give sufficient area for prepainting.
+      // Note this value is specified with an ideal contents scale in mind. That
+      // is, the ideal tiling would use this value as the padding.
+      // TODO(vmpstr): Figure out a better number that doesn't depend on scale.
       tiling_interest_area_padding(3000),
       skewport_target_time_in_seconds(1.0f),
       skewport_extrapolation_limit_in_screen_pixels(2000),