cc:: Add remote mode to the compositor

cc/proto/compositor_message_to_impl.proto

Index: cc/proto/compositor_message_to_impl.proto
diff --git a/cc/proto/compositor_message_to_impl.proto b/cc/proto/compositor_message_to_impl.proto
new file mode 100644
index 0000000000000000000000000000000000000000..8d173164f19b1d89fc0b81d1c94da7874dd3fdb6
--- /dev/null
+++ b/cc/proto/compositor_message_to_impl.proto
@@ -0,0 +1,55 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.

[vmpstr, 2016/01/11 21:50:15]

2016

[Khushal, 2016/01/13 02:07:11]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+import "layer_tree_settings.proto";
+
+package cc.proto;
+
+// Control messages sent to the impl side of the compositor (client) from the
+// main side of the compositor (server).
+// Note: Unless specified in a comment, all fields in a message are required,
+// even if listed as optional.
+message CompositorMessageToImpl {
+  enum Type {
+    Unknown = 0;

[vmpstr, 2016/01/11 21:50:15]

I think we went with SHOUT_CASE for enums
(https://codereview.chromium.org/1492533003/)

Can you also add a comment for the unkown case (ie when you would expect this)

[Khushal, 2016/01/13 02:07:12]

Done.

+
+    // Client Initialization: When the remote server starts up it sends a
+    // CompositorMessageToImpl of Type::InitializeImpl to the client. This

[vmpstr, 2016/01/11 21:50:14]

nit: s/Type::/type /

[Khushal, 2016/01/13 02:07:12]

Done.

+    // message should be processed by the embedder of the client compositor to
+    // create the Remote Client LayerTreeHost. The compositor protocol
+    // guarantees that this will be the first message sent to the client. No
+    // messages can be sent from the client before the server is started.
+    InitializeImpl = 1;
+
+    // Client Shutdown: When the remote server is shutting down it sends a
+    // CompositorMessageToImpl of type::CloseImpl to the client. The message
+    // should be processed by the embedder of the client compositor to destroy
+    // the Remote Client LayerTreeHost. This is guaranteed to be the last
+    // message sent to the client. No messages can be sent from the client after
+    // the server has been shutdown.
+    CloseImpl = 2;
+
+    // Informs the client that a fling animation on the server has stopped.
+    MainThreadHasStoppedFlingingOnImpl = 3;

[vmpstr, 2016/01/11 21:50:15]

Is there a corresponding start fling message? Maybe can either add the start
fling here as well or delay adding the stop one until later?

[Khushal, 2016/01/13 02:07:12]

Right now the message types here are basically serializing the communication
between ProxyMain and ProxyImpl. The stop message comes from blink, I don't know
if they need to or have a method to inform the compositor about when the fling
starts.

Right now I think this call just gets piped to the InputHandlerClient and we
probably don't need to use it right now, but since the ChannelMain interface
which will define these types will develop alongside the changes for the
threaded case, we can add the start call when its required to be added to both?

+  }
+
+  optional Type message_type = 1;
+
+  // Only one of the following fields will be set per CompositorMessageToImpl.
+
+  // Set for message Type::InitializeImpl.
+  optional InitializeImpl initialize_impl_message = 2;
+}
+
+message InitializeImpl {
+  // The embedder of the remote client compositor should process the

[vmpstr, 2016/01/11 21:50:15]

nit: Can you move this comment before "message InitializeImpl"

[Khushal, 2016/01/13 02:07:11]

Done.

+  // InitializeImpl message to retrieve the LayerTreeSettings sent from the
+  // server.
+  // The settings sent from the server may be modified by the embedder.

[vmpstr, 2016/01/11 21:50:15]

formatting nit: move this line to the previous one

[Khushal, 2016/01/13 02:07:11]

Done.

+  optional LayerTreeSettings layer_tree_settings = 1;
+}