Added LayerTreeHostImpl::layerTreeAsJson which serializes a layer tree

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index c295e920432a6a22acd80869e3e09b513de998f1..6a6a98232351ef72aa1b89a4d6cd186e85e518e7 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -8,6 +8,7 @@
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
+#include "base/json/json_writer.h"
 #include "base/stl_util.h"
 #include "cc/append_quads_data.h"
 #include "cc/damage_tracker.h"
@@ -1552,6 +1553,17 @@ std::string LayerTreeHostImpl::layerTreeAsText() const
     return str;
 }
 
+std::string LayerTreeHostImpl::layerTreeAsJson() const
+{
+    std::string str;
+    if (rootLayer()) {
+        scoped_ptr<base::Value> json(rootLayer()->layerTreeAsJson());
+        base::JSONWriter::WriteWithOptions(
+            json.get(), base::JSONWriter::OPTIONS_PRETTY_PRINT, &str);
+    }
+    return str;
+}
+
 void LayerTreeHostImpl::dumpRenderSurfaces(std::string* str, int indent, const LayerImpl* layer) const
 {
     if (layer->renderSurface())