Reland of placing allocate bitmap IPC messages with a new Mojo interface.

content/common/render_message_filter.mojom

Index: content/common/render_message_filter.mojom
diff --git a/content/common/render_message_filter.mojom b/content/common/render_message_filter.mojom
index be6a9a97cdfc6f5322e8923b59f7a2d83f535ed7..df4cd7e6b93be7ec12a6d2403dcd35b774395d14 100644
--- a/content/common/render_message_filter.mojom
+++ b/content/common/render_message_filter.mojom
@@ -6,6 +6,7 @@
 
 import "content/common/native_types.mojom";
 import "content/public/common/window_container_type.mojom";
+import "gpu/ipc/common/mailbox.mojom";
 import "third_party/WebKit/public/platform/referrer.mojom";
 import "third_party/WebKit/public/web/window_features.mojom";
 import "ui/base/mojo/window_open_disposition.mojom";
@@ -92,4 +93,15 @@
   // Similar to CreateWidget except the widget is a full screen window.
   [Sync] CreateFullscreenWidget(int32 opener_id)
       => (int32 route_id);
+
+  // The 2 following methods belong to a future CC related mojom.
+  // For now they need to be part of this channel associated interface to
+  // prevent running into message ordering issues (CC trying to access a shared
+  // bitmap before the registration message below made it to the browser).
+  //
+  // Informs the browser that the child allocated a shared bitmap.
+  AllocatedSharedBitmap(handle<shared_buffer> buffer, gpu.mojom.Mailbox id);
+
+  // Informs the browser that the child deleted a shared bitmap.
+  DeletedSharedBitmap(gpu.mojom.Mailbox id);
 };