Make tile size a function of the device scale factor.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 6d8aaa614416f7b54b4c6a1c3fb1b7ee04d38a5d..a5c066591f605c54cccb9d5c58fac159f4c0e88e 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -89,6 +89,7 @@
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "ui/gfx/geometry/point_conversions.h"
 #include "ui/gfx/geometry/rect_conversions.h"
+#include "ui/gfx/geometry/safe_integer_conversions.h"
 #include "ui/gfx/geometry/scroll_offset.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/geometry/vector2d_conversions.h"
@@ -2408,7 +2409,7 @@ void LayerTreeHostImpl::SetViewportSize(const gfx::Size& device_viewport_size) {
   active_tree_->set_needs_update_draw_properties();
 }
 
-const gfx::Rect LayerTreeHostImpl::ViewportRectForTilePriority() const {
+gfx::Rect LayerTreeHostImpl::ViewportRectForTilePriority() const {
   if (viewport_rect_for_tile_priority_.IsEmpty())
     return DeviceViewport();
 
@@ -2416,9 +2417,37 @@ const gfx::Rect LayerTreeHostImpl::ViewportRectForTilePriority() const {
 }
 
 gfx::Size LayerTreeHostImpl::DrawViewportSize() const {
+  // XXX DIE DIE DIE DIE

[enne (OOO), 2016/06/28 18:39:02]

https://www.youtube.com/watch?v=UrHVBfSaPtA

   return DeviceViewport().size();
 }
 
+gfx::Size LayerTreeHostImpl::GetStableScreenSize(

[enne (OOO), 2016/06/28 18:39:01]

How does this relate to gfx::DeviceDisplayInfo::GetPhysicalDisplay*? Is it the
same, always?

+    const LayerTreeImpl* tree) const {
+  // TODO(crbug.com/622885): Get a stable screen size for any platform from
+  // the embedder.
+
+  // This size does not include an external viewport size.
+  int width = device_viewport_size_.width();
+  int height = device_viewport_size_.height();
+  if (tree->top_controls_shrink_blink_size())
+    height += gfx::ToCeiledInt(tree->top_controls_height() *
+                               tree->device_scale_factor());
+
+  if (external_viewport_.IsEmpty())
+    return gfx::Size(width, height);
+
+  int external_width = external_viewport_.width();
+  int external_height = external_viewport_.height();
+  if (tree->top_controls_shrink_blink_size())
+    external_height += gfx::ToCeiledInt(tree->top_controls_height() *
+                                        tree->device_scale_factor());
+
+  // Take the smaller of the two. An external viewport may be much larger than
+  // what will actually be on screen, or much smaller.
+  return gfx::Size(std::min(width, external_width),
+                   std::min(height, external_height));
+}
+
 gfx::Rect LayerTreeHostImpl::DeviceViewport() const {
   if (external_viewport_.IsEmpty())
     return gfx::Rect(device_viewport_size_);