Compositor thread plumbing for layout rectangle debug info.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index f8882291dd32f9a0b1e6451b0d23485091f77786..092300b08a48725f889f57bd823b3d830465d498 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -5,6 +5,7 @@
 #include "cc/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
+#include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ -155,6 +156,11 @@ void LayerImpl::SetScrollParent(LayerImpl* parent) {
   scroll_parent_ = parent;
 }
 
+void LayerImpl::SetDebugInfo(
+    scoped_refptr<base::debug::ConvertableToTraceFormat> other) {
+  debug_info_ = other;
+}
+
 void LayerImpl::SetScrollChildren(std::set<LayerImpl*>* children) {
   if (scroll_children_.get() == children)
     return;
@@ -590,6 +596,8 @@ void LayerImpl::PushPropertiesTo(LayerImpl* layer) {
   // Reset any state that should be cleared for the next update.
   stacking_order_changed_ = false;
   update_rect_ = gfx::RectF();
+
+  layer->SetDebugInfo(debug_info_);
 }
 
 base::DictionaryValue* LayerImpl::LayerTreeAsJson() const {
@@ -1364,6 +1372,19 @@ void LayerImpl::AsValueInto(base::DictionaryValue* state) const {
     if (layer_animation_controller_->AnimatedBoundsForBox(box, &inflated))
       state->Set("animated_bounds", MathUtil::AsValue(inflated).release());
   }
+
+  if (debug_info_.get()) {
+    std::string str;
+    debug_info_->AppendAsTraceFormat(&str);
+    base::JSONReader json_reader;
+    // Parsing the JSON and re-encoding it is not very efficient,
+    // but it's the simplest way to achieve the desired effect, which
+    // is to output:
+    // {..., layout_rects: [{geometry_rect: ...}, ...], ...}
+    // rather than:
+    // {layout_rects: "[{geometry_rect: ...}, ...]", ...}
+    state->Set("layout_rects", json_reader.ReadToValue(str));
+  }
 }
 
 size_t LayerImpl::GPUMemoryUsageInBytes() const { return 0; }