cc: Clean up max frames/swaps pending usage.

All output surfaces used by the Renderer and UI should
only need a max swaps pending of 1, especially considering
Surfaces and CompositorTimingHistory don't support
multiple queued frames.

The output suface used by the cc::Display, however, may
have more than 1 swap pending - especially on platforms like
CrOS where the SwapAck is deferred until the buffer is actually
displayed.

This patch:
1) Changes the default max pending frames/swaps from 2 to 1.
2) Changes Blimp to have only 1 pending frame.
3) DCHECKS that all Renderers and UIs have a max swaps pending of 1.
4) Sets the default value in the constructor of
   OutpuSurface::Capabilities, rather than through
   an extra check for zero + init.

BUG=525756
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1435133004

Cr-Commit-Position: refs/heads/master@{#360283}

5 files changed, 7 insertions, 25 deletions

diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 072086f..eb2c3e1 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -193,10 +193,6 @@ void Scheduler::SetNeedsPrepareTiles() {
   ProcessScheduledActions();
 }
 
-void Scheduler::SetMaxSwapsPending(int max) {
-  state_machine_.SetMaxSwapsPending(max);
-}
-
 void Scheduler::DidSwapBuffers() {
   state_machine_.DidSwapBuffers();
 
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index 5773bc4..6f8ba1e 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -95,7 +95,6 @@ class CC_EXPORT Scheduler : public BeginFrameObserverBase {
 
   void SetNeedsPrepareTiles();
 
-  void SetMaxSwapsPending(int max);
   void DidSwapBuffers();
   void DidSwapBuffersComplete();
 
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index 01ac8cb..d770689 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -13,6 +13,11 @@
 
 namespace cc {
 
+namespace {
+// Surfaces and CompositorTimingHistory don't support more than 1 pending swap.
+const int kMaxPendingSwaps = 1;
+}  // namespace
+
 SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
     : settings_(settings),
       output_surface_state_(OUTPUT_SURFACE_NONE),
@@ -32,7 +37,6 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       invalidate_output_surface_funnel_(false),
       prepare_tiles_funnel_(0),
       consecutive_checkerboard_animations_(0),
-      max_pending_swaps_(1),
       pending_swaps_(0),
       swaps_with_current_output_surface_(0),
       needs_redraw_(false),
@@ -217,7 +221,6 @@ void SchedulerStateMachine::AsValueInto(
                     invalidate_output_surface_funnel_);
   state->SetInteger("consecutive_checkerboard_animations",
                     consecutive_checkerboard_animations_);
-  state->SetInteger("max_pending_swaps_", max_pending_swaps_);
   state->SetInteger("pending_swaps_", pending_swaps_);
   state->SetInteger("swaps_with_current_output_surface",
                     swaps_with_current_output_surface_);
@@ -912,7 +915,7 @@ bool SchedulerStateMachine::main_thread_missed_last_deadline() const {
 }
 
 bool SchedulerStateMachine::SwapThrottled() const {
-  return pending_swaps_ >= max_pending_swaps_;
+  return pending_swaps_ >= kMaxPendingSwaps;
 }
 
 void SchedulerStateMachine::SetVisible(bool visible) {
@@ -957,17 +960,12 @@ void SchedulerStateMachine::SetNeedsPrepareTiles() {
     needs_prepare_tiles_ = true;
   }
 }
-
-void SchedulerStateMachine::SetMaxSwapsPending(int max) {
-  max_pending_swaps_ = max;
-}
-
 void SchedulerStateMachine::DidSwapBuffers() {
   TRACE_EVENT_ASYNC_BEGIN0("cc", "Scheduler:pending_swaps", this);
   pending_swaps_++;
   swaps_with_current_output_surface_++;
 
-  DCHECK_LE(pending_swaps_, max_pending_swaps_);
+  DCHECK_LE(pending_swaps_, kMaxPendingSwaps);
 
   did_perform_swap_in_last_draw_ = true;
   last_frame_number_swap_performed_ = current_frame_number_;
diff --git a/cc/scheduler/scheduler_state_machine.h b/cc/scheduler/scheduler_state_machine.h
index 17fdf98..3c32dc6 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -174,9 +174,6 @@ class CC_EXPORT SchedulerStateMachine {
   // PrepareTiles will occur shortly (even if no redraw is required).
   void SetNeedsPrepareTiles();
 
-  // Sets how many swaps can be pending to the OutputSurface.
-  void SetMaxSwapsPending(int max);
-
   // If the scheduler attempted to draw and swap, this provides feedback
   // regarding whether or not the swap actually occured. We might skip the
   // swap when there is not damage, for example.
diff --git a/cc/scheduler/scheduler_unittest.cc b/cc/scheduler/scheduler_unittest.cc
index 6bdf5dd..362946f 100644
--- a/cc/scheduler/scheduler_unittest.cc
+++ b/cc/scheduler/scheduler_unittest.cc
@@ -1471,7 +1471,6 @@ TEST_F(SchedulerTest, MainFrameNotSkippedAfterLateCommit_DrawEstimateTooLong) {
 void SchedulerTest::ImplFrameSkippedAfterLateSwapAck(
     bool swap_ack_before_deadline) {
   // To get into a high latency state, this test disables automatic swap acks.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Draw and swap for first BeginFrame
@@ -1595,7 +1594,6 @@ TEST_F(SchedulerTest,
   SetUpScheduler(true);
 
   // To get into a high latency state, this test disables automatic swap acks.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Even if every estimate related to the main thread is slow, we should
@@ -1659,7 +1657,6 @@ TEST_F(SchedulerTest,
 
 void SchedulerTest::ImplFrameIsNotSkippedAfterLateSwapAck() {
   // To get into a high latency state, this test disables automatic swap acks.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Draw and swap for first BeginFrame
@@ -1770,7 +1767,6 @@ TEST_F(SchedulerTest,
   fake_compositor_timing_history_->SetAllEstimatesTo(slow_duration);
 
   // To get into a high latency state, this test disables automatic swap acks.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Impl thread hits deadline before commit finishes to make
@@ -1899,7 +1895,6 @@ TEST_F(
 
   // Disables automatic swap acks so this test can force swap ack throttling
   // to simulate a blocked Browser ui thread.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Get a new active tree in main-thread high latency mode and put us
@@ -1970,7 +1965,6 @@ TEST_F(SchedulerTest,
 
   // Disables automatic swap acks so this test can force swap ack throttling
   // to simulate a blocked Browser ui thread.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Start a new commit in main-thread high latency mode and hold off on
@@ -2051,7 +2045,6 @@ TEST_F(
 
   // Disables automatic swap acks so this test can force swap ack throttling
   // to simulate a blocked Browser ui thread.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // Start a new commit in main-thread high latency mode and hold off on
@@ -2447,7 +2440,6 @@ void SchedulerTest::BeginFramesNotFromClient_SwapThrottled(
   fake_compositor_timing_history_->SetDrawDurationEstimate(base::TimeDelta());
 
   // To test swap ack throttling, this test disables automatic swap acks.
-  scheduler_->SetMaxSwapsPending(1);
   client_->SetAutomaticSwapAck(false);
 
   // SetNeedsBeginMainFrame should begin the frame on the next BeginImplFrame.