Remove "mixin" from BeginFrameSource/Observer base classes.

cc/surfaces/display_scheduler.cc

 // 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 "cc/surfaces/display_scheduler.h"
 
 #include <vector>
 
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 104 matching lines @@
 
   needs_draw_ = false;
   entire_display_damaged_ = false;
   all_active_child_surfaces_ready_to_draw_ =
       child_surface_ids_to_expect_damage_from_.empty();
 
   expect_damage_from_root_surface_ = root_surface_damaged_;
   root_surface_damaged_ = false;
 }
 
-bool DisplayScheduler::OnBeginFrameMixInDelegate(const BeginFrameArgs& args) {
+bool DisplayScheduler::OnBeginFrameDerivedImpl(const BeginFrameArgs& args) {
   base::TimeTicks now = base::TimeTicks::Now();
   TRACE_EVENT2("cc", "DisplayScheduler::BeginFrame", "args", args.AsValue(),
                "now", now);
 
   // If we get another BeginFrame before the previous deadline,
   // synchronously trigger the previous deadline before progressing.
   if (inside_begin_frame_deadline_interval_) {
     OnBeginFrameDeadline();
   }
 
@@ skipping 142 matching lines @@
 }
 
 void DisplayScheduler::DidSwapBuffersComplete() {
   pending_swaps_--;
   TRACE_EVENT1("cc", "DisplayScheduler::DidSwapBuffersComplete",
                "pending_frames", pending_swaps_);
   ScheduleBeginFrameDeadline();
 }
 
 }  // namespace cc