Keep track of coalesced events in main thread event queue

content/common/input_messages.h

 // Copyright (c) 2013 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.
 
 // IPC messages for input events and other messages that require processing in
 // order relative to input events.
 // Multiply-included message file, hence no include guard.
 
 #include "base/strings/string16.h"
 #include "build/build_config.h"
@@ skipping 117 matching lines @@
 
 IPC_STRUCT_TRAITS_BEGIN(content::InputEventAck)
   IPC_STRUCT_TRAITS_MEMBER(source)
   IPC_STRUCT_TRAITS_MEMBER(type)
   IPC_STRUCT_TRAITS_MEMBER(state)
   IPC_STRUCT_TRAITS_MEMBER(latency)
   IPC_STRUCT_TRAITS_MEMBER(overscroll)
   IPC_STRUCT_TRAITS_MEMBER(unique_touch_event_id)
 IPC_STRUCT_TRAITS_END()
 
-// Sends an input event to the render widget.
-IPC_MESSAGE_ROUTED3(InputMsg_HandleInputEvent,
-                    IPC::WebInputEventPointer /* event */,
-                    ui::LatencyInfo /* latency_info */,
-                    content::InputEventDispatchType)
+// Sends an input event to the render widget. The input event in general
+// contains a list of coalesced events and one event that is representative of
+// all those events (https://w3c.github.io/pointerevents/extension.html).
+IPC_MESSAGE_ROUTED4(
+    InputMsg_HandleInputEvent,
+    IPC::WebInputEventPointer /* event */,
+    std::vector<IPC::WebInputEventPointer> /* coalesced events */,
+    ui::LatencyInfo /* latency_info */,
+    content::InputEventDispatchType)
 
 // Sends the cursor visibility state to the render widget.
 IPC_MESSAGE_ROUTED1(InputMsg_CursorVisibilityChange,
                     bool /* is_visible */)
 
 // Sets the text composition to be between the given start and end offsets in
 // the currently focused editable field.
 IPC_MESSAGE_ROUTED3(InputMsg_SetCompositionFromExistingText,
     int /* start */,
     int /* end */,
@@ skipping 167 matching lines @@
 // This IPC message sends the character bounds after every composition change
 // to always have correct bound info.
 IPC_MESSAGE_ROUTED2(InputHostMsg_ImeCompositionRangeChanged,
                     gfx::Range /* composition range */,
                     std::vector<gfx::Rect> /* character bounds */)
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent InputMsg, then ifdefs for platform specific InputMsg, then
 // platform independent InputHostMsg, then ifdefs for platform specific
 // InputHostMsg.