Define cc::RendererCapabilities in its own header, fix up includes

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 3105e6f48eaa6c0cd0eb2c380d9285495aaa4059..5aee8352df472bec23ac478d49fd0e7b77df3123 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -14,9 +14,12 @@
 #include "cc/base/scoped_ptr_vector.h"
 #include "cc/base/swap_promise.h"
 #include "cc/base/synced_property.h"
+#include "cc/input/layer_selection_bound.h"
 #include "cc/layers/layer_impl.h"
+#include "cc/output/begin_frame_args.h"
 #include "cc/output/renderer.h"
 #include "cc/resources/ui_resource_client.h"
+#include "cc/trees/layer_tree_host_impl.h"
 
 namespace base {
 namespace trace_event {
@@ -32,7 +35,6 @@ class FrameRateCounter;
 class HeadsUpDisplayLayerImpl;
 class LayerScrollOffsetDelegateProxy;
 class LayerTreeDebugState;
-class LayerTreeHostImpl;
 class LayerTreeImpl;
 class LayerTreeSettings;
 class MemoryHistory;