Allow the renderer process to map textures from one context into another.

content/renderer/gpu/command_buffer_proxy.cc

Index: content/renderer/gpu/command_buffer_proxy.cc
===================================================================
--- content/renderer/gpu/command_buffer_proxy.cc	(revision 94701)
+++ content/renderer/gpu/command_buffer_proxy.cc	(working copy)
@@ -349,6 +349,27 @@
     swap_buffers_callback_->Run();
 }
 
+bool CommandBufferProxy::MapExternalResource(
+    gpu::resource_type::ResourceType resource_type,
+    uint32 resource_source_id,
+    CommandBufferProxy* source_command_buffer,
+    uint32 resource_dest_id) {
+  if (last_state_.error != gpu::error::kNoError)
+    return false;
+
+  if (!Send(new GpuCommandBufferMsg_MapExternalResource(
+      route_id_,
+      resource_type,
+      resource_source_id,
+      source_command_buffer ?
+          source_command_buffer->route_id() : MSG_ROUTING_NONE,
+      resource_dest_id))) {
+    return false;
+  }
+
+  return true;
+}
+
 bool CommandBufferProxy::SetParent(CommandBufferProxy* parent_command_buffer,
                                    uint32 parent_texture_id) {
   if (last_state_.error != gpu::error::kNoError)