Allow null begin frame sources in cc::Scheduler

cc/scheduler/scheduler_unittest.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 <stddef.h>
 
 #include <string>
 #include <vector>
@@ skipping 3151 matching lines @@
 
   EXPECT_SCOPED(AdvanceFrame());
   EXPECT_ACTION("WillBeginImplFrame", client_, 0, 1);
   EXPECT_TRUE(scheduler_->BeginImplFrameDeadlinePending());
   EXPECT_TRUE(scheduler_->begin_frames_expected());
   client_->Reset();
   task_runner().RunPendingTasks();  // Run posted deadline.
   EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 0, 1);
 }
 
+TEST_F(SchedulerTest, SwitchFrameSourceToNullInsideDeadline) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+
+  scheduler_->SetNeedsRedraw();
+  EXPECT_SINGLE_ACTION("AddObserver(this)", client_);
+  client_->Reset();
+
+  EXPECT_SCOPED(AdvanceFrame());
+  EXPECT_SINGLE_ACTION("WillBeginImplFrame", client_);
+  client_->Reset();
+
+  // Switch to a null frame source.
+  scheduler_->SetBeginFrameSource(nullptr);
+  EXPECT_SINGLE_ACTION("RemoveObserver(this)", client_);
+  client_->Reset();
+
+  EXPECT_TRUE(scheduler_->BeginImplFrameDeadlinePending());
+  task_runner().RunPendingTasks();  // Run posted deadline.
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 0, 1);
+  EXPECT_FALSE(scheduler_->begin_frames_expected());
+  EXPECT_FALSE(scheduler_->BeginImplFrameDeadlinePending());
+  client_->Reset();
+
+  // AdvanceFrame helper can't be used here because there's no deadline posted.
+  scheduler_->SetNeedsRedraw();
+  EXPECT_FALSE(scheduler_->BeginImplFrameDeadlinePending());
+  EXPECT_NO_ACTION(client_);
+  client_->Reset();
+
+  scheduler_->SetNeedsBeginMainFrame();
+  EXPECT_FALSE(scheduler_->BeginImplFrameDeadlinePending());
+  EXPECT_NO_ACTION(client_);
+  client_->Reset();
+
+  // Switch back to the same source, make sure frames continue to be produced.
+  scheduler_->SetBeginFrameSource(fake_external_begin_frame_source_.get());
+  EXPECT_SINGLE_ACTION("AddObserver(this)", client_);
+  EXPECT_FALSE(scheduler_->BeginImplFrameDeadlinePending());
+  client_->Reset();
+
+  EXPECT_SCOPED(AdvanceFrame());
+  EXPECT_ACTION("WillBeginImplFrame", client_, 0, 2);
+  EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 1, 2);
+  EXPECT_TRUE(scheduler_->BeginImplFrameDeadlinePending());
+  client_->Reset();
+
+  task_runner().RunPendingTasks();
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 0, 1);
+}
+
 // This test maskes sure that switching a frame source when not observing
 // such as when not visible also works.
 TEST_F(SchedulerTest, SwitchFrameSourceWhenNotObserving) {
   scheduler_settings_.use_external_begin_frame_source = true;
   SetUpScheduler(true);
 
   // SetNeedsBeginMainFrame should begin the frame on the next BeginImplFrame.
   scheduler_->SetNeedsBeginMainFrame();
   EXPECT_SINGLE_ACTION("AddObserver(this)", client_);
   client_->Reset();
@@ skipping 617 matching lines @@
 }
 
 TEST_F(SchedulerTest, BeginMainFrameOnCriticalPath_AHS) {
   EXPECT_FALSE(BeginMainFrameOnCriticalPath(
       SMOOTHNESS_TAKES_PRIORITY,
       ScrollHandlerState::SCROLL_AFFECTS_SCROLL_HANDLER, kSlowDuration));
 }
 
 }  // namespace
 }  // namespace cc