sync compositor: Reduce begin frame sync IPC overhead

content/common/android/sync_compositor_messages.h

 // 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.
 
 #include <stddef.h>
 
 #include "base/memory/shared_memory_handle.h"
 #include "cc/output/begin_frame_args.h"
 #include "cc/output/compositor_frame.h"
 #include "content/common/content_export.h"
@@ skipping 42 matching lines @@
 
   gfx::Size size;
   gfx::Rect clip;
   gfx::Transform transform;
 };
 
 struct SyncCompositorCommonRendererParams {
   SyncCompositorCommonRendererParams();
   ~SyncCompositorCommonRendererParams();
 
-  unsigned int version;
+  // Allow copy.
+  SyncCompositorCommonRendererParams(
+      const SyncCompositorCommonRendererParams& other);
+  SyncCompositorCommonRendererParams& operator=(
+      const SyncCompositorCommonRendererParams& other);
+
+  unsigned int version = 0u;
   gfx::ScrollOffset total_scroll_offset;
   gfx::ScrollOffset max_scroll_offset;
   gfx::SizeF scrollable_size;
-  float page_scale_factor;
-  float min_page_scale_factor;
-  float max_page_scale_factor;
-  bool need_animate_scroll;
-  uint32_t need_invalidate_count;
-  uint32_t did_activate_pending_tree_count;
+  float page_scale_factor = 0.f;
+  float min_page_scale_factor = 0.f;
+  float max_page_scale_factor = 0.f;
+  bool need_animate_scroll = false;
+  uint32_t need_invalidate_count = 0u;
+  uint32_t did_activate_pending_tree_count = 0u;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_ANDROID_SYNC_COMPOSITOR_MESSAGES_H_
 
 // Multiply-included message file, hence no include guard.
 
 #undef IPC_MESSAGE_EXPORT
 #define IPC_MESSAGE_EXPORT CONTENT_EXPORT
@@ skipping 29 matching lines @@
   IPC_STRUCT_TRAITS_MEMBER(max_page_scale_factor)
   IPC_STRUCT_TRAITS_MEMBER(need_animate_scroll)
   IPC_STRUCT_TRAITS_MEMBER(need_invalidate_count)
   IPC_STRUCT_TRAITS_MEMBER(did_activate_pending_tree_count)
 IPC_STRUCT_TRAITS_END()
 
 // Messages sent from the browser to the renderer.
 // Synchronous IPCs are allowed here to the renderer compositor thread. See
 // design doc https://goo.gl/Tn81FW and crbug.com/526842 for details.
 
-IPC_SYNC_MESSAGE_ROUTED0_1(SyncCompositorMsg_SynchronizeRendererState,
-                           content::SyncCompositorCommonRendererParams)
+IPC_SYNC_MESSAGE_CONTROL1_1(
+    SyncCompositorMsg_SynchronizeRendererState,
+    std::vector<int> /* routing ids*/,
+    std::vector<content::SyncCompositorCommonRendererParams>)
 
 IPC_MESSAGE_ROUTED1(SyncCompositorMsg_ComputeScroll,
                     base::TimeTicks);
 
 IPC_SYNC_MESSAGE_ROUTED1_3(SyncCompositorMsg_DemandDrawHw,
                            content::SyncCompositorDemandDrawHwParams,
                            content::SyncCompositorCommonRendererParams,
                            uint32_t /* output_surface_id */,
                            cc::CompositorFrame)
 
@@ skipping 24 matching lines @@
 
 IPC_MESSAGE_ROUTED1(SyncCompositorMsg_SetScroll, gfx::ScrollOffset);
 
 // -----------------------------------------------------------------------------
 // Messages sent from the renderer to the browser.
 
 IPC_MESSAGE_ROUTED0(SyncCompositorHostMsg_OutputSurfaceCreated);
 
 IPC_MESSAGE_ROUTED1(SyncCompositorHostMsg_UpdateState,
                     content::SyncCompositorCommonRendererParams)