Add support for (de)serializing LayerTreeHost.

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
new file mode 100644
index 0000000000000000000000000000000000000000..432c1f60cb0583bf3ab7b42aa2c3a23f5572df70
--- /dev/null
+++ b/cc/proto/layer_tree_host.proto
@@ -0,0 +1,56 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+import "layer.proto";
+import "layer_selection_bound.proto";
+import "layer_tree_settings.proto";
+import "layer_tree_debug_state.proto";
+import "property_tree.proto";
+import "size.proto";
+import "vector2df.proto";
+
+package cc.proto;
+
+option optimize_for = LITE_RUNTIME;
+
+message LayerTreeHost {
+  // Not all members of LayerTreeHost are serialized, as they are not helpful
+  // for remote usage. See implementation of
+  // cc::LayerTreeHost::ToProtobufForCommit for details.
+  optional bool needs_full_tree_sync = 1;
+  optional bool needs_meta_info_recomputation = 2;
+  optional int32 source_frame_number = 3;
+  optional int32 meta_information_sequence_number = 4;
+  optional LayerNode root_layer = 5;
+  optional LayerUpdate layer_updates = 6;
+  optional int32 hud_layer_id = 7;
+  optional LayerTreeDebugState debug_state = 8;
+  optional Size device_viewport_size = 9;
+  optional bool top_controls_shrink_blink_size = 10;
+  optional float top_controls_height = 11;
+  optional float top_controls_shown_ratio = 12;
+  optional float device_scale_factor = 13;
+  optional float painted_device_scale_factor = 14;
+  optional float page_scale_factor = 15;
+  optional float min_page_scale_factor = 16;
+  optional float max_page_scale_factor = 17;
+  optional Vector2dF elastic_overscroll = 18;
+  optional bool has_gpu_rasterization_trigger = 19;
+  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_id_namespace = 32;
+  optional uint32 next_surface_sequence = 33;
+}