x11: Make PlatformEvent-related methods optional in XEventDispatcher interface

XEventDispatcher implementation *can* optionally be associated to a
PlatformEventDispatcher, however in most cases it is not the case and 3 methods
must be overridden with a empty/stub implementation. This CL changes
XEventDispatcher, adding default empty implementation for PlatformEvent-related
functions, making it easier and more intuitive implementing it.

Bug: 789065
Change-Id: Icdb501133817038a536b108f8a0d8556ff3389f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1710242
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680107}

ui/events/platform/x11/x11_event_source_libevent.cc

@@ -250,4 +250,12 @@ void X11EventSourceLibevent::OnFileCanWriteWithoutBlocking(int fd) {
   NOTREACHED();
 }
 
+void XEventDispatcher::CheckCanDispatchNextPlatformEvent(XEvent* xev) {}
+
+void XEventDispatcher::PlatformEventDispatchFinished() {}
+
+PlatformEventDispatcher* XEventDispatcher::GetPlatformEventDispatcher() {
+  return nullptr;
+}
+
 }  // namespace ui

ui/events/platform/x11/x11_event_source_libevent.h

@@ -20,25 +20,25 @@ namespace ui {
 // X11 currently.
 class EVENTS_EXPORT XEventDispatcher {
  public:
+  // Sends XEvent to XEventDispatcher for handling. Returns true if the XEvent
+  // was dispatched, otherwise false. After the first XEventDispatcher returns
+  // true XEvent dispatching stops.
+  virtual bool DispatchXEvent(XEvent* xevent) = 0;
+
   // XEventDispatchers can be used to test if they are able to process next
   // translated event sent by a PlatformEventSource. If so, they must make a
   // promise internally to process next event sent by PlatformEventSource.
-  virtual void CheckCanDispatchNextPlatformEvent(XEvent* xev) = 0;
+  virtual void CheckCanDispatchNextPlatformEvent(XEvent* xev);
 
   // Tells that an event has been dispatched and an event handling promise must
   // be removed.
-  virtual void PlatformEventDispatchFinished() = 0;
+  virtual void PlatformEventDispatchFinished();
 
   // Returns PlatformEventDispatcher if this XEventDispatcher is associated with
   // a PlatformEventDispatcher as well. Used to explicitly add a
   // PlatformEventDispatcher during a call from an XEventDispatcher to
   // AddXEventDispatcher.
-  virtual PlatformEventDispatcher* GetPlatformEventDispatcher() = 0;
-
-  // Sends XEvent to XEventDispatcher for handling. Returns true if the XEvent
-  // was dispatched, otherwise false. After the first XEventDispatcher returns
-  // true XEvent dispatching stops.
-  virtual bool DispatchXEvent(XEvent* xevent) = 0;
+  virtual PlatformEventDispatcher* GetPlatformEventDispatcher();
 
  protected:
   virtual ~XEventDispatcher() {}

ui/ozone/platform/x11/gl_surface_glx_ozone.cc

@@ -30,14 +30,6 @@ void GLSurfaceGLXOzone::UnregisterEvents() {
     event_source->RemoveXEventDispatcher(this);
 }
 
-void GLSurfaceGLXOzone::CheckCanDispatchNextPlatformEvent(XEvent* xev) {}
-
-void GLSurfaceGLXOzone::PlatformEventDispatchFinished() {}
-
-PlatformEventDispatcher* GLSurfaceGLXOzone::GetPlatformEventDispatcher() {
-  return nullptr;
-}
-
 bool GLSurfaceGLXOzone::DispatchXEvent(XEvent* event) {
   if (!CanHandleEvent(event))
     return false;

ui/ozone/platform/x11/gl_surface_glx_ozone.h

@@ -11,8 +11,6 @@
 
 namespace ui {
 
-class PlatformEventDispatcher;
-
 // Ozone specific implementation of GLX surface. Registers as a XEventDispatcher
 // to handle XEvents.
 class GLSurfaceGLXOzone : public gl::NativeViewGLSurfaceGLX,
@@ -28,9 +26,6 @@ class GLSurfaceGLXOzone : public gl::NativeViewGLSurfaceGLX,
   void UnregisterEvents() override;
 
   // XEventDispatcher:
-  void CheckCanDispatchNextPlatformEvent(XEvent* xev) override;
-  void PlatformEventDispatchFinished() override;
-  PlatformEventDispatcher* GetPlatformEventDispatcher() override;
   bool DispatchXEvent(XEvent* xevent) override;
 
  private: