Allow null begin frame sources in cc::Scheduler

cc/scheduler/scheduler.cc

 // Copyright 2011 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/scheduler/scheduler.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
@@ skipping 55 matching lines @@
   begin_retro_frame_closure_ =
       base::Bind(&Scheduler::BeginRetroFrame, weak_factory_.GetWeakPtr());
   begin_impl_frame_deadline_closure_ = base::Bind(
       &Scheduler::OnBeginImplFrameDeadline, weak_factory_.GetWeakPtr());
 
   SetBeginFrameSource(begin_frame_source);
   ProcessScheduledActions();
 }
 
 Scheduler::~Scheduler() {
-  if (observing_begin_frame_source_)
-    begin_frame_source_->RemoveObserver(this);
+  SetBeginFrameSource(nullptr);
 }
 
 base::TimeTicks Scheduler::Now() const {
   base::TimeTicks now = base::TimeTicks::Now();
   TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler.now"),
                "Scheduler::Now",
                "now",
                now);
   return now;
 }
@@ skipping 20 matching lines @@
   ProcessScheduledActions();
 }
 
 void Scheduler::NotifyReadyToDraw() {
   // Future work might still needed for crbug.com/352894.
   state_machine_.NotifyReadyToDraw();
   ProcessScheduledActions();
 }
 
 void Scheduler::SetBeginFrameSource(BeginFrameSource* source) {
-  DCHECK(source);
   if (source == begin_frame_source_)
     return;
   if (begin_frame_source_ && observing_begin_frame_source_)
     begin_frame_source_->RemoveObserver(this);
   begin_frame_source_ = source;
+  if (!begin_frame_source_)
+    return;
   if (observing_begin_frame_source_)
     begin_frame_source_->AddObserver(this);
 }
 
 void Scheduler::SetNeedsBeginMainFrame() {
   state_machine_.SetNeedsBeginMainFrame();
   ProcessScheduledActions();
 }
 
 void Scheduler::SetNeedsOneBeginImplFrame() {
@@ skipping 104 matching lines @@
   client_->SendBeginMainFrameNotExpectedSoon();
 }
 
 void Scheduler::SetupNextBeginFrameIfNeeded() {
   // Never call SetNeedsBeginFrames if the frame source already has the right
   // value.
   if (observing_begin_frame_source_ != state_machine_.BeginFrameNeeded()) {
     if (state_machine_.BeginFrameNeeded()) {
       // Call AddObserver as soon as possible.
       observing_begin_frame_source_ = true;
-      begin_frame_source_->AddObserver(this);
+      if (begin_frame_source_)
+        begin_frame_source_->AddObserver(this);
       devtools_instrumentation::NeedsBeginFrameChanged(layer_tree_host_id_,
                                                        true);
     } else if (state_machine_.begin_impl_frame_state() ==
                SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE) {
       // Call RemoveObserver in between frames only.
       observing_begin_frame_source_ = false;
-      begin_frame_source_->RemoveObserver(this);
+      if (begin_frame_source_)
+        begin_frame_source_->RemoveObserver(this);
       BeginImplFrameNotExpectedSoon();
       devtools_instrumentation::NeedsBeginFrameChanged(layer_tree_host_id_,
                                                        false);
     }
   }
 
   PostBeginRetroFrameIfNeeded();
 }
 
 void Scheduler::OnBeginFrameSourcePausedChanged(bool paused) {
@@ skipping 108 matching lines @@
   while (!begin_retro_frame_args_.empty()) {
     const BeginFrameArgs& args = begin_retro_frame_args_.front();
     base::TimeTicks expiration_time = args.deadline;
     if (now <= expiration_time)
       break;
     TRACE_EVENT_INSTANT2(
         "cc", "Scheduler::BeginRetroFrame discarding", TRACE_EVENT_SCOPE_THREAD,
         "expiration_time - now", (expiration_time - now).InMillisecondsF(),
         "BeginFrameArgs", begin_retro_frame_args_.front().AsValue());
     begin_retro_frame_args_.pop_front();
-    begin_frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
+    if (begin_frame_source_)
+      begin_frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
   }
 
   if (begin_retro_frame_args_.empty()) {
     TRACE_EVENT_INSTANT0("cc",
                          "Scheduler::BeginRetroFrames all expired",
                          TRACE_EVENT_SCOPE_THREAD);
   } else {
     BeginFrameArgs front = begin_retro_frame_args_.front();
     begin_retro_frame_args_.pop_front();
     BeginImplFrameWithDeadline(front);
@@ skipping 72 matching lines @@
                                                  bmf_to_activate_estimate);
 
   if (ShouldRecoverMainLatency(adjusted_args, can_activate_before_deadline)) {
     TRACE_EVENT_INSTANT0("cc", "SkipBeginMainFrameToReduceLatency",
                          TRACE_EVENT_SCOPE_THREAD);
     state_machine_.SetSkipNextBeginMainFrameToReduceLatency();
   } else if (ShouldRecoverImplLatency(adjusted_args,
                                       can_activate_before_deadline)) {
     TRACE_EVENT_INSTANT0("cc", "SkipBeginImplFrameToReduceLatency",
                          TRACE_EVENT_SCOPE_THREAD);
-    begin_frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
+    if (begin_frame_source_)
+      begin_frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
     return;
   }
 
   BeginImplFrame(adjusted_args);
 
   // The deadline will be scheduled in ProcessScheduledActions.
   state_machine_.OnBeginImplFrameDeadlinePending();
   ProcessScheduledActions();
 }
 
@@ skipping 11 matching lines @@
   compositor_timing_history_->WillFinishImplFrame(
       state_machine_.needs_redraw());
   FinishImplFrame();
 }
 
 void Scheduler::FinishImplFrame() {
   state_machine_.OnBeginImplFrameIdle();
   ProcessScheduledActions();
 
   client_->DidFinishImplFrame();
-  begin_frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
+  if (begin_frame_source_)
+    begin_frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
   begin_impl_frame_tracker_.Finish();
 }
 
 // BeginImplFrame starts a compositor frame that will wait up until a deadline
 // for a BeginMainFrame+activation to complete before it times out and draws
 // any asynchronous animation and scroll/pinch updates.
 void Scheduler::BeginImplFrame(const BeginFrameArgs& args) {
   DCHECK_EQ(state_machine_.begin_impl_frame_state(),
             SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE);
   DCHECK(!BeginImplFrameDeadlinePending());
@@ skipping 343 matching lines @@
 }
 
 bool Scheduler::IsBeginMainFrameSentOrStarted() const {
   return (state_machine_.begin_main_frame_state() ==
               SchedulerStateMachine::BEGIN_MAIN_FRAME_STATE_SENT ||
           state_machine_.begin_main_frame_state() ==
               SchedulerStateMachine::BEGIN_MAIN_FRAME_STATE_STARTED);
 }
 
 }  // namespace cc