Setup LayerTree class, refactor 2 functions from LayerTreeHost to it.

cc/proto/layer_tree_host.proto

Index: cc/proto/layer_tree_host.proto
diff --git a/cc/proto/layer_tree_host.proto b/cc/proto/layer_tree_host.proto
index 71bbcf529dfcb3490ed9d3e42291b3618c02b792..76639950df5acea7beba2eb4d9314021f6c2ffbc 100644
--- a/cc/proto/layer_tree_host.proto
+++ b/cc/proto/layer_tree_host.proto
@@ -7,6 +7,7 @@ syntax = "proto2";
 import "display_item.proto";
 import "layer.proto";
 import "layer_selection_bound.proto";
+import "layer_tree.proto";
 import "layer_tree_debug_state.proto";
 import "property_tree.proto";
 import "size.proto";
@@ -51,21 +52,20 @@ message LayerTreeHost {
   optional bool content_is_suitable_for_gpu_rasterization = 20;
   optional uint32 background_color = 21; /* SkColor */
   optional bool has_transparent_background = 22;
-  optional bool in_paint_layer_contents = 23;
-  optional int32 id = 24;
-  optional bool next_commit_forces_redraw = 25;
-  optional int32 overscroll_elasticity_layer_id = 26;
-  optional int32 page_scale_layer_id = 27;
-  optional int32 inner_viewport_scroll_layer_id = 28;
-  optional int32 outer_viewport_scroll_layer_id = 29;
-  optional LayerSelection selection = 30;
-  optional PropertyTrees property_trees = 31;
-  optional uint32 surface_client_id = 32;
-  optional uint32 next_surface_sequence = 33;
-  optional uint32 wheel_event_listener_properties = 34;
-  optional bool have_scroll_event_handlers = 35;
-  optional uint32 touch_start_or_move_event_listener_properties = 36;
-  repeated int32 layers_that_should_push_properties = 37;
-  optional uint32 touch_end_or_cancel_event_listener_properties = 38;
-  optional SkPictures pictures = 39;
+  optional int32 id = 23;
+  optional bool next_commit_forces_redraw = 24;
+  optional int32 overscroll_elasticity_layer_id = 25;
+  optional int32 page_scale_layer_id = 26;
+  optional int32 inner_viewport_scroll_layer_id = 27;
+  optional int32 outer_viewport_scroll_layer_id = 28;
+  optional LayerSelection selection = 29;
+  optional PropertyTrees property_trees = 30;
+  optional uint32 surface_client_id = 31;
+  optional uint32 next_surface_sequence = 32;
+  optional uint32 wheel_event_listener_properties = 33;
+  optional bool have_scroll_event_handlers = 34;
+  optional uint32 touch_start_or_move_event_listener_properties = 35;
+  optional LayerTree layer_tree = 36;
+  optional uint32 touch_end_or_cancel_event_listener_properties = 37;
+  optional SkPictures pictures = 38;
 }