Decouple EventWithLatencyInfo from WebInputEventTraits

content/common/input/event_with_latency_info.h

 // Copyright 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.
 
 #ifndef CONTENT_COMMON_INPUT_EVENT_WITH_LATENCY_INFO_H_
 #define CONTENT_COMMON_INPUT_EVENT_WITH_LATENCY_INFO_H_
 
+#include "base/compiler_specific.h"

[tdresser, 2016/06/30 14:16:39]

Are we using this?

[tapted, 2016/07/01 02:53:45]

Yep - for WARN_UNUSED_RESULT in the original code

+#include "base/logging.h"
+#include "content/common/content_export.h"
+#include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/events/latency_info.h"
 
-#include "content/common/input/web_input_event_traits.h"
+namespace content {
+namespace internal {
 
-namespace blink {
-class WebGestureEvent;
-class WebMouseEvent;
-class WebMouseWheelEvent;
-class WebTouchEvent;
-}
+bool CONTENT_EXPORT CanCoalesce(const blink::WebMouseEvent& event_to_coalesce,
+                                const blink::WebMouseEvent& event);
+void CONTENT_EXPORT Coalesce(const blink::WebMouseEvent& event_to_coalesce,
+                             blink::WebMouseEvent* event);
+bool CONTENT_EXPORT
+CanCoalesce(const blink::WebMouseWheelEvent& event_to_coalesce,
+            const blink::WebMouseWheelEvent& event);
+void CONTENT_EXPORT Coalesce(const blink::WebMouseWheelEvent& event_to_coalesce,
+                             blink::WebMouseWheelEvent* event);
+bool CONTENT_EXPORT CanCoalesce(const blink::WebTouchEvent& event_to_coalesce,
+                                const blink::WebTouchEvent& event);
+void CONTENT_EXPORT Coalesce(const blink::WebTouchEvent& event_to_coalesce,
+                             blink::WebTouchEvent* event);
+bool CONTENT_EXPORT CanCoalesce(const blink::WebGestureEvent& event_to_coalesce,
+                                const blink::WebGestureEvent& event);
+void CONTENT_EXPORT Coalesce(const blink::WebGestureEvent& event_to_coalesce,
+                             blink::WebGestureEvent* event);
 
-namespace content {
+}  // namespace internal

[tapted, 2016/06/30 12:13:45]

This wasn't my first choice.. In http://crrev.com/2091213002 I got this working
with extern templates which hid all this (and the bodies of the
[Can]CoalesceWith member functions) in the .cc file. But extern templates are
kinda confusing, and it ran afoul of compiler bugs - different ones both on MSVC
and clang/gcc - details in http://crbug.com/623844.

I found workarounds for the compiler bugs, but this is nicer in some ways too
since you get a compiler error rather than a linker error if you try call
CanCoalesceWith on an unsupported type (client code can even add new supported
types).

 
 template <typename T>
 class EventWithLatencyInfo {
  public:
   T event;
   mutable ui::LatencyInfo latency;
 
   explicit EventWithLatencyInfo(const T& e) : event(e) {}
 
   EventWithLatencyInfo(const T& e, const ui::LatencyInfo& l)
       : event(e), latency(l) {}
 
   EventWithLatencyInfo() {}
 
   bool CanCoalesceWith(const EventWithLatencyInfo& other)
       const WARN_UNUSED_RESULT {
-    return WebInputEventTraits::CanCoalesce(other.event, event);
+    if (other.event.type != event.type)
+      return false;
+
+    DCHECK_EQ(sizeof(T), event.size);
+    DCHECK_EQ(sizeof(T), other.event.size);
+
+    return internal::CanCoalesce(other.event, event);
   }
 
   void CoalesceWith(const EventWithLatencyInfo& other) {
     // |other| should be a newer event than |this|.
     if (other.latency.trace_id() >= 0 && latency.trace_id() >= 0)
       DCHECK_GT(other.latency.trace_id(), latency.trace_id());
-    WebInputEventTraits::Coalesce(other.event, &event);
+
+    // New events get coalesced into older events, and the newer timestamp
+    // should always be preserved.
+    const double time_stamp_seconds = other.event.timeStampSeconds;
+    internal::Coalesce(other.event, &event);
+    event.timeStampSeconds = time_stamp_seconds;
+
     // When coalescing two input events, we keep the oldest LatencyInfo
     // for Telemetry latency tests, since it will represent the longest
     // latency.
     other.latency = latency;
     other.latency.set_coalesced();
   }
 };
 
 typedef EventWithLatencyInfo<blink::WebGestureEvent>
     GestureEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebMouseWheelEvent>
     MouseWheelEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebMouseEvent>
     MouseEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebTouchEvent>
     TouchEventWithLatencyInfo;
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_INPUT_EVENT_WITH_LATENCY_INFO_H_