Revert "Delete CC."

cc/scheduler/scheduler_state_machine.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_state_machine.h"
+
+#include "base/format_macros.h"
+#include "base/logging.h"
+#include "base/strings/stringprintf.h"
+#include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_argument.h"
+#include "base/values.h"
+#include "ui/gfx/frame_time.h"
+
+namespace cc {
+
+SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
+    : settings_(settings),
+      output_surface_state_(OUTPUT_SURFACE_LOST),
+      begin_impl_frame_state_(BEGIN_IMPL_FRAME_STATE_IDLE),
+      commit_state_(COMMIT_STATE_IDLE),
+      forced_redraw_state_(FORCED_REDRAW_STATE_IDLE),
+      commit_count_(0),
+      current_frame_number_(0),
+      last_frame_number_animate_performed_(-1),
+      last_frame_number_swap_performed_(-1),
+      last_frame_number_swap_requested_(-1),
+      last_frame_number_begin_main_frame_sent_(-1),
+      animate_funnel_(false),
+      perform_swap_funnel_(false),
+      request_swap_funnel_(false),
+      send_begin_main_frame_funnel_(false),
+      prepare_tiles_funnel_(0),
+      consecutive_checkerboard_animations_(0),
+      max_pending_swaps_(1),
+      pending_swaps_(0),
+      needs_redraw_(false),
+      needs_animate_(false),
+      needs_prepare_tiles_(false),
+      needs_commit_(false),
+      inside_poll_for_anticipated_draw_triggers_(false),
+      visible_(false),
+      can_start_(false),
+      can_draw_(false),
+      has_pending_tree_(false),
+      pending_tree_is_ready_for_activation_(false),
+      active_tree_needs_first_draw_(false),
+      did_create_and_initialize_first_output_surface_(false),
+      impl_latency_takes_priority_(false),
+      skip_next_begin_main_frame_to_reduce_latency_(false),
+      skip_begin_main_frame_to_reduce_latency_(false),
+      continuous_painting_(false),
+      children_need_begin_frames_(false),
+      defer_commits_(false),
+      last_commit_had_no_updates_(false) {
+}
+
+const char* SchedulerStateMachine::OutputSurfaceStateToString(
+    OutputSurfaceState state) {
+  switch (state) {
+    case OUTPUT_SURFACE_ACTIVE:
+      return "OUTPUT_SURFACE_ACTIVE";
+    case OUTPUT_SURFACE_LOST:
+      return "OUTPUT_SURFACE_LOST";
+    case OUTPUT_SURFACE_CREATING:
+      return "OUTPUT_SURFACE_CREATING";
+    case OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT:
+      return "OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT";
+    case OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION:
+      return "OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION";
+  }
+  NOTREACHED();
+  return "???";
+}
+
+const char* SchedulerStateMachine::BeginImplFrameStateToString(
+    BeginImplFrameState state) {
+  switch (state) {
+    case BEGIN_IMPL_FRAME_STATE_IDLE:
+      return "BEGIN_IMPL_FRAME_STATE_IDLE";
+    case BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING:
+      return "BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING";
+    case BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME:
+      return "BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME";
+    case BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE:
+      return "BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE";
+  }
+  NOTREACHED();
+  return "???";
+}
+
+const char* SchedulerStateMachine::CommitStateToString(CommitState state) {
+  switch (state) {
+    case COMMIT_STATE_IDLE:
+      return "COMMIT_STATE_IDLE";
+    case COMMIT_STATE_BEGIN_MAIN_FRAME_SENT:
+      return "COMMIT_STATE_BEGIN_MAIN_FRAME_SENT";
+    case COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED:
+      return "COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED";
+    case COMMIT_STATE_READY_TO_COMMIT:
+      return "COMMIT_STATE_READY_TO_COMMIT";
+    case COMMIT_STATE_WAITING_FOR_ACTIVATION:
+      return "COMMIT_STATE_WAITING_FOR_ACTIVATION";
+    case COMMIT_STATE_WAITING_FOR_DRAW:
+      return "COMMIT_STATE_WAITING_FOR_DRAW";
+  }
+  NOTREACHED();
+  return "???";
+}
+
+const char* SchedulerStateMachine::ForcedRedrawOnTimeoutStateToString(
+    ForcedRedrawOnTimeoutState state) {
+  switch (state) {
+    case FORCED_REDRAW_STATE_IDLE:
+      return "FORCED_REDRAW_STATE_IDLE";
+    case FORCED_REDRAW_STATE_WAITING_FOR_COMMIT:
+      return "FORCED_REDRAW_STATE_WAITING_FOR_COMMIT";
+    case FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION:
+      return "FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION";
+    case FORCED_REDRAW_STATE_WAITING_FOR_DRAW:
+      return "FORCED_REDRAW_STATE_WAITING_FOR_DRAW";
+  }
+  NOTREACHED();
+  return "???";
+}
+
+const char* SchedulerStateMachine::ActionToString(Action action) {
+  switch (action) {
+    case ACTION_NONE:
+      return "ACTION_NONE";
+    case ACTION_ANIMATE:
+      return "ACTION_ANIMATE";
+    case ACTION_SEND_BEGIN_MAIN_FRAME:
+      return "ACTION_SEND_BEGIN_MAIN_FRAME";
+    case ACTION_COMMIT:
+      return "ACTION_COMMIT";
+    case ACTION_ACTIVATE_SYNC_TREE:
+      return "ACTION_ACTIVATE_SYNC_TREE";
+    case ACTION_DRAW_AND_SWAP_IF_POSSIBLE:
+      return "ACTION_DRAW_AND_SWAP_IF_POSSIBLE";
+    case ACTION_DRAW_AND_SWAP_FORCED:
+      return "ACTION_DRAW_AND_SWAP_FORCED";
+    case ACTION_DRAW_AND_SWAP_ABORT:
+      return "ACTION_DRAW_AND_SWAP_ABORT";
+    case ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
+      return "ACTION_BEGIN_OUTPUT_SURFACE_CREATION";
+    case ACTION_PREPARE_TILES:
+      return "ACTION_PREPARE_TILES";
+  }
+  NOTREACHED();
+  return "???";
+}
+
+scoped_refptr<base::trace_event::ConvertableToTraceFormat>
+SchedulerStateMachine::AsValue() const {
+  scoped_refptr<base::trace_event::TracedValue> state =
+      new base::trace_event::TracedValue();
+  AsValueInto(state.get());
+  return state;
+}
+
+void SchedulerStateMachine::AsValueInto(
+    base::trace_event::TracedValue* state) const {
+  state->BeginDictionary("major_state");
+  state->SetString("next_action", ActionToString(NextAction()));
+  state->SetString("begin_impl_frame_state",
+                   BeginImplFrameStateToString(begin_impl_frame_state_));
+  state->SetString("commit_state", CommitStateToString(commit_state_));
+  state->SetString("output_surface_state_",
+                   OutputSurfaceStateToString(output_surface_state_));
+  state->SetString("forced_redraw_state",
+                   ForcedRedrawOnTimeoutStateToString(forced_redraw_state_));
+  state->EndDictionary();
+
+  state->BeginDictionary("minor_state");
+  state->SetInteger("commit_count", commit_count_);
+  state->SetInteger("current_frame_number", current_frame_number_);
+  state->SetInteger("last_frame_number_animate_performed",
+                    last_frame_number_animate_performed_);
+  state->SetInteger("last_frame_number_swap_performed",
+                    last_frame_number_swap_performed_);
+  state->SetInteger("last_frame_number_swap_requested",
+                    last_frame_number_swap_requested_);
+  state->SetInteger("last_frame_number_begin_main_frame_sent",
+                    last_frame_number_begin_main_frame_sent_);
+  state->SetBoolean("funnel: animate_funnel", animate_funnel_);
+  state->SetBoolean("funnel: perform_swap_funnel", perform_swap_funnel_);
+  state->SetBoolean("funnel: request_swap_funnel", request_swap_funnel_);
+  state->SetBoolean("funnel: send_begin_main_frame_funnel",
+                    send_begin_main_frame_funnel_);
+  state->SetInteger("funnel: prepare_tiles_funnel", prepare_tiles_funnel_);
+  state->SetInteger("consecutive_checkerboard_animations",
+                    consecutive_checkerboard_animations_);
+  state->SetInteger("max_pending_swaps_", max_pending_swaps_);
+  state->SetInteger("pending_swaps_", pending_swaps_);
+  state->SetBoolean("needs_redraw", needs_redraw_);
+  state->SetBoolean("needs_animate_", needs_animate_);
+  state->SetBoolean("needs_prepare_tiles", needs_prepare_tiles_);
+  state->SetBoolean("needs_commit", needs_commit_);
+  state->SetBoolean("visible", visible_);
+  state->SetBoolean("can_start", can_start_);
+  state->SetBoolean("can_draw", can_draw_);
+  state->SetBoolean("has_pending_tree", has_pending_tree_);
+  state->SetBoolean("pending_tree_is_ready_for_activation",
+                    pending_tree_is_ready_for_activation_);
+  state->SetBoolean("active_tree_needs_first_draw",
+                    active_tree_needs_first_draw_);
+  state->SetBoolean("did_create_and_initialize_first_output_surface",
+                    did_create_and_initialize_first_output_surface_);
+  state->SetBoolean("impl_latency_takes_priority",
+                    impl_latency_takes_priority_);
+  state->SetBoolean("main_thread_is_in_high_latency_mode",
+                    MainThreadIsInHighLatencyMode());
+  state->SetBoolean("skip_begin_main_frame_to_reduce_latency",
+                    skip_begin_main_frame_to_reduce_latency_);
+  state->SetBoolean("skip_next_begin_main_frame_to_reduce_latency",
+                    skip_next_begin_main_frame_to_reduce_latency_);
+  state->SetBoolean("continuous_painting", continuous_painting_);
+  state->SetBoolean("children_need_begin_frames", children_need_begin_frames_);
+  state->SetBoolean("defer_commits", defer_commits_);
+  state->EndDictionary();
+}
+
+void SchedulerStateMachine::AdvanceCurrentFrameNumber() {
+  current_frame_number_++;
+
+  animate_funnel_ = false;
+  perform_swap_funnel_ = false;
+  request_swap_funnel_ = false;
+  send_begin_main_frame_funnel_ = false;
+
+  // "Drain" the PrepareTiles funnel.
+  if (prepare_tiles_funnel_ > 0)
+    prepare_tiles_funnel_--;
+
+  skip_begin_main_frame_to_reduce_latency_ =
+      skip_next_begin_main_frame_to_reduce_latency_;
+  skip_next_begin_main_frame_to_reduce_latency_ = false;
+}
+
+bool SchedulerStateMachine::PendingDrawsShouldBeAborted() const {
+  // These are all the cases where we normally cannot or do not want to draw
+  // but, if needs_redraw_ is true and we do not draw to make forward progress,
+  // we might deadlock with the main thread.
+  // This should be a superset of PendingActivationsShouldBeForced() since
+  // activation of the pending tree is blocked by drawing of the active tree and
+  // the main thread might be blocked on activation of the most recent commit.
+  if (PendingActivationsShouldBeForced())
+    return true;
+
+  // Additional states where we should abort draws.
+  if (!can_draw_)
+    return true;
+  return false;
+}
+
+bool SchedulerStateMachine::PendingActivationsShouldBeForced() const {
+  // There is no output surface to trigger our activations.
+  // If we do not force activations to make forward progress, we might deadlock
+  // with the main thread.
+  if (output_surface_state_ == OUTPUT_SURFACE_LOST)
+    return true;
+
+  // If we're not visible, we should force activation.
+  // Since we set RequiresHighResToDraw when becoming visible, we ensure that we
+  // don't checkerboard until all visible resources are done. Furthermore, if we
+  // do keep the pending tree around, when becoming visible we might activate
+  // prematurely causing RequiresHighResToDraw flag to be reset. In all cases,
+  // we can simply activate on becoming invisible since we don't need to draw
+  // the active tree when we're in this state.
+  if (!visible_)
+    return true;
+
+  return false;
+}
+
+bool SchedulerStateMachine::ShouldBeginOutputSurfaceCreation() const {
+  // Don't try to initialize too early.
+  if (!can_start_)
+    return false;
+
+  // We only want to start output surface initialization after the
+  // previous commit is complete.
+  if (commit_state_ != COMMIT_STATE_IDLE)
+    return false;
+
+  // Make sure the BeginImplFrame from any previous OutputSurfaces
+  // are complete before creating the new OutputSurface.
+  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_IDLE)
+    return false;
+
+  // We want to clear the pipline of any pending draws and activations
+  // before starting output surface initialization. This allows us to avoid
+  // weird corner cases where we abort draws or force activation while we
+  // are initializing the output surface.
+  if (active_tree_needs_first_draw_ || has_pending_tree_)
+    return false;
+
+  // We need to create the output surface if we don't have one and we haven't
+  // started creating one yet.
+  return output_surface_state_ == OUTPUT_SURFACE_LOST;
+}
+
+bool SchedulerStateMachine::ShouldDraw() const {
+  // If we need to abort draws, we should do so ASAP since the draw could
+  // be blocking other important actions (like output surface initialization),
+  // from occuring. If we are waiting for the first draw, then perfom the
+  // aborted draw to keep things moving. If we are not waiting for the first
+  // draw however, we don't want to abort for no reason.
+  if (PendingDrawsShouldBeAborted())
+    return active_tree_needs_first_draw_;
+
+  // Do not draw too many times in a single frame. It's okay that we don't check
+  // this before checking for aborted draws because aborted draws do not request
+  // a swap.
+  if (request_swap_funnel_)
+    return false;
+
+  // Don't draw if we are waiting on the first commit after a surface.
+  if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE)
+    return false;
+
+  // Do not queue too many swaps.
+  if (pending_swaps_ >= max_pending_swaps_)
+    return false;
+
+  // Except for the cases above, do not draw outside of the BeginImplFrame
+  // deadline.
+  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
+    return false;
+
+  // Only handle forced redraws due to timeouts on the regular deadline.
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
+    return true;
+
+  return needs_redraw_;
+}
+
+bool SchedulerStateMachine::ShouldActivatePendingTree() const {
+  // There is nothing to activate.
+  if (!has_pending_tree_)
+    return false;
+
+  // We should not activate a second tree before drawing the first one.
+  // Even if we need to force activation of the pending tree, we should abort
+  // drawing the active tree first.
+  if (active_tree_needs_first_draw_)
+    return false;
+
+  // If we want to force activation, do so ASAP.
+  if (PendingActivationsShouldBeForced())
+    return true;
+
+  // At this point, only activate if we are ready to activate.
+  return pending_tree_is_ready_for_activation_;
+}
+
+bool SchedulerStateMachine::ShouldAnimate() const {
+  // Do not animate too many times in a single frame.
+  if (animate_funnel_)
+    return false;
+
+  // Don't animate if we are waiting on the first commit after a surface.
+  if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE)
+    return false;
+
+  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING &&
+      begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
+    return false;
+
+  return needs_redraw_ || needs_animate_;
+}
+
+bool SchedulerStateMachine::CouldSendBeginMainFrame() const {
+  // Do not send begin main frame too many times in a single frame.
+  if (send_begin_main_frame_funnel_)
+    return false;
+
+  if (!needs_commit_)
+    return false;
+
+  // We can not perform commits if we are not visible.
+  if (!visible_)
+    return false;
+
+  // Do not make a new commits when it is deferred.
+  if (defer_commits_)
+    return false;
+
+  return true;
+}
+
+bool SchedulerStateMachine::ShouldSendBeginMainFrame() const {
+  if (!CouldSendBeginMainFrame())
+    return false;
+
+  // Only send BeginMainFrame when there isn't another commit pending already.
+  if (commit_state_ != COMMIT_STATE_IDLE)
+    return false;
+
+  // Don't send BeginMainFrame early if we are prioritizing the active tree
+  // because of impl_latency_takes_priority_.
+  if (impl_latency_takes_priority_ &&
+      (has_pending_tree_ || active_tree_needs_first_draw_)) {
+    return false;
+  }
+
+  // We should not send BeginMainFrame while we are in
+  // BEGIN_IMPL_FRAME_STATE_IDLE since we might have new
+  // user input arriving soon.
+  // TODO(brianderson): Allow sending BeginMainFrame while idle when the main
+  // thread isn't consuming user input.
+  if (begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_IDLE &&
+      BeginFrameNeeded())
+    return false;
+
+  // We need a new commit for the forced redraw. This honors the
+  // single commit per interval because the result will be swapped to screen.
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT)
+    return true;
+
+  // We shouldn't normally accept commits if there isn't an OutputSurface.
+  if (!HasInitializedOutputSurface())
+    return false;
+
+  // SwapAck throttle the BeginMainFrames unless we just swapped.
+  // TODO(brianderson): Remove this restriction to improve throughput.
+  bool just_swapped_in_deadline =
+      begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE &&
+      perform_swap_funnel_;
+  if (pending_swaps_ >= max_pending_swaps_ && !just_swapped_in_deadline)
+    return false;
+
+  if (skip_begin_main_frame_to_reduce_latency_)
+    return false;
+
+  return true;
+}
+
+bool SchedulerStateMachine::ShouldCommit() const {
+  if (commit_state_ != COMMIT_STATE_READY_TO_COMMIT)
+    return false;
+
+  // We must not finish the commit until the pending tree is free.
+  if (has_pending_tree_) {
+    DCHECK(settings_.main_frame_before_activation_enabled);
+    return false;
+  }
+
+  // Prioritize drawing the previous commit before finishing the next commit.
+  if (active_tree_needs_first_draw_)
+    return false;
+
+  return true;
+}
+
+bool SchedulerStateMachine::ShouldPrepareTiles() const {
+  // PrepareTiles only really needs to be called immediately after commit
+  // and then periodically after that. Use a funnel to make sure we average
+  // one PrepareTiles per BeginImplFrame in the long run.
+  if (prepare_tiles_funnel_ > 0)
+    return false;
+
+  // Limiting to once per-frame is not enough, since we only want to
+  // prepare tiles _after_ draws. Polling for draw triggers and
+  // begin-frame are mutually exclusive, so we limit to these two cases.
+  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE &&
+      !inside_poll_for_anticipated_draw_triggers_)
+    return false;
+  return needs_prepare_tiles_;
+}
+
+SchedulerStateMachine::Action SchedulerStateMachine::NextAction() const {
+  if (ShouldActivatePendingTree())
+    return ACTION_ACTIVATE_SYNC_TREE;
+  if (ShouldCommit())
+    return ACTION_COMMIT;
+  if (ShouldAnimate())
+    return ACTION_ANIMATE;
+  if (ShouldDraw()) {
+    if (PendingDrawsShouldBeAborted())
+      return ACTION_DRAW_AND_SWAP_ABORT;
+    else if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
+      return ACTION_DRAW_AND_SWAP_FORCED;
+    else
+      return ACTION_DRAW_AND_SWAP_IF_POSSIBLE;
+  }
+  if (ShouldPrepareTiles())
+    return ACTION_PREPARE_TILES;
+  if (ShouldSendBeginMainFrame())
+    return ACTION_SEND_BEGIN_MAIN_FRAME;
+  if (ShouldBeginOutputSurfaceCreation())
+    return ACTION_BEGIN_OUTPUT_SURFACE_CREATION;
+  return ACTION_NONE;
+}
+
+void SchedulerStateMachine::UpdateState(Action action) {
+  switch (action) {
+    case ACTION_NONE:
+      return;
+
+    case ACTION_ACTIVATE_SYNC_TREE:
+      UpdateStateOnActivation();
+      return;
+
+    case ACTION_ANIMATE:
+      DCHECK(!animate_funnel_);
+      last_frame_number_animate_performed_ = current_frame_number_;
+      animate_funnel_ = true;
+      needs_animate_ = false;
+      // TODO(skyostil): Instead of assuming this, require the client to tell
+      // us.
+      SetNeedsRedraw();
+      return;
+
+    case ACTION_SEND_BEGIN_MAIN_FRAME:
+      DCHECK(!has_pending_tree_ ||
+             settings_.main_frame_before_activation_enabled);
+      DCHECK(visible_);
+      DCHECK(!send_begin_main_frame_funnel_);
+      commit_state_ = COMMIT_STATE_BEGIN_MAIN_FRAME_SENT;
+      needs_commit_ = false;
+      send_begin_main_frame_funnel_ = true;
+      last_frame_number_begin_main_frame_sent_ =
+          current_frame_number_;
+      return;
+
+    case ACTION_COMMIT: {
+      bool commit_has_no_updates = false;
+      UpdateStateOnCommit(commit_has_no_updates);
+      return;
+    }
+
+    case ACTION_DRAW_AND_SWAP_FORCED:
+    case ACTION_DRAW_AND_SWAP_IF_POSSIBLE: {
+      bool did_request_swap = true;
+      UpdateStateOnDraw(did_request_swap);
+      return;
+    }
+
+    case ACTION_DRAW_AND_SWAP_ABORT: {
+      bool did_request_swap = false;
+      UpdateStateOnDraw(did_request_swap);
+      return;
+    }
+
+    case ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
+      DCHECK_EQ(output_surface_state_, OUTPUT_SURFACE_LOST);
+      output_surface_state_ = OUTPUT_SURFACE_CREATING;
+
+      // The following DCHECKs make sure we are in the proper quiescent state.
+      // The pipeline should be flushed entirely before we start output
+      // surface creation to avoid complicated corner cases.
+      DCHECK_EQ(commit_state_, COMMIT_STATE_IDLE);
+      DCHECK(!has_pending_tree_);
+      DCHECK(!active_tree_needs_first_draw_);
+      return;
+
+    case ACTION_PREPARE_TILES:
+      UpdateStateOnPrepareTiles();
+      return;
+  }
+}
+
+void SchedulerStateMachine::UpdateStateOnCommit(bool commit_has_no_updates) {
+  commit_count_++;
+
+  if (!commit_has_no_updates)
+    animate_funnel_ = false;
+
+  if (commit_has_no_updates || settings_.main_frame_before_activation_enabled) {
+    commit_state_ = COMMIT_STATE_IDLE;
+  } else if (settings_.impl_side_painting) {
+    commit_state_ = COMMIT_STATE_WAITING_FOR_ACTIVATION;
+  } else {
+    commit_state_ = settings_.main_thread_should_always_be_low_latency
+                        ? COMMIT_STATE_WAITING_FOR_DRAW
+                        : COMMIT_STATE_IDLE;
+  }
+
+  // If we are impl-side-painting but the commit was aborted, then we behave
+  // mostly as if we are not impl-side-painting since there is no pending tree.
+  has_pending_tree_ = settings_.impl_side_painting && !commit_has_no_updates;
+
+  // Update state related to forced draws.
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT) {
+    forced_redraw_state_ = has_pending_tree_
+                               ? FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION
+                               : FORCED_REDRAW_STATE_WAITING_FOR_DRAW;
+  }
+
+  // Update the output surface state.
+  DCHECK_NE(output_surface_state_, OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION);
+  if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT) {
+    if (has_pending_tree_) {
+      output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION;
+    } else {
+      output_surface_state_ = OUTPUT_SURFACE_ACTIVE;
+      needs_redraw_ = true;
+    }
+  }
+
+  // Update state if we have a new active tree to draw, or if the active tree
+  // was unchanged but we need to do a forced draw.
+  if (!has_pending_tree_ &&
+      (!commit_has_no_updates ||
+       forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)) {
+    needs_redraw_ = true;
+    active_tree_needs_first_draw_ = true;
+  }
+
+  // This post-commit work is common to both completed and aborted commits.
+  pending_tree_is_ready_for_activation_ = false;
+
+  if (continuous_painting_)
+    needs_commit_ = true;
+  last_commit_had_no_updates_ = commit_has_no_updates;
+}
+
+void SchedulerStateMachine::UpdateStateOnActivation() {
+  if (commit_state_ == COMMIT_STATE_WAITING_FOR_ACTIVATION) {
+    commit_state_ = settings_.main_thread_should_always_be_low_latency
+                        ? COMMIT_STATE_WAITING_FOR_DRAW
+                        : COMMIT_STATE_IDLE;
+  }
+
+  if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION)
+    output_surface_state_ = OUTPUT_SURFACE_ACTIVE;
+
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION)
+    forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_DRAW;
+
+  has_pending_tree_ = false;
+  pending_tree_is_ready_for_activation_ = false;
+  active_tree_needs_first_draw_ = true;
+  needs_redraw_ = true;
+}
+
+void SchedulerStateMachine::UpdateStateOnDraw(bool did_request_swap) {
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
+    forced_redraw_state_ = FORCED_REDRAW_STATE_IDLE;
+
+  if (commit_state_ == COMMIT_STATE_WAITING_FOR_DRAW)
+    commit_state_ = COMMIT_STATE_IDLE;
+
+  needs_redraw_ = false;
+  active_tree_needs_first_draw_ = false;
+
+  if (did_request_swap) {
+    DCHECK(!request_swap_funnel_);
+    request_swap_funnel_ = true;
+    last_frame_number_swap_requested_ = current_frame_number_;
+  }
+}
+
+void SchedulerStateMachine::UpdateStateOnPrepareTiles() {
+  needs_prepare_tiles_ = false;
+}
+
+void SchedulerStateMachine::SetSkipNextBeginMainFrameToReduceLatency() {
+  TRACE_EVENT_INSTANT0("cc",
+                       "Scheduler: SkipNextBeginMainFrameToReduceLatency",
+                       TRACE_EVENT_SCOPE_THREAD);
+  skip_next_begin_main_frame_to_reduce_latency_ = true;
+}
+
+bool SchedulerStateMachine::BeginFrameNeededForChildren() const {
+  if (HasInitializedOutputSurface())
+    return children_need_begin_frames_;
+
+  return false;
+}
+
+bool SchedulerStateMachine::BeginFrameNeeded() const {
+  // We can't handle BeginFrames when output surface isn't initialized.
+  // TODO(brianderson): Support output surface creation inside a BeginFrame.
+  if (!HasInitializedOutputSurface())
+    return false;
+
+  if (SupportsProactiveBeginFrame()) {
+    return (BeginFrameNeededToAnimateOrDraw() ||
+            BeginFrameNeededForChildren() ||
+            ProactiveBeginFrameWanted());
+  }
+
+  // Proactive BeginFrames are bad for the synchronous compositor because we
+  // have to draw when we get the BeginFrame and could end up drawing many
+  // duplicate frames if our new frame isn't ready in time.
+  // To poll for state with the synchronous compositor without having to draw,
+  // we rely on ShouldPollForAnticipatedDrawTriggers instead.
+  // Synchronous compositor doesn't have a browser.
+  DCHECK(!children_need_begin_frames_);
+  return BeginFrameNeededToAnimateOrDraw();
+}
+
+bool SchedulerStateMachine::ShouldPollForAnticipatedDrawTriggers() const {
+  // ShouldPollForAnticipatedDrawTriggers is what we use in place of
+  // ProactiveBeginFrameWanted when we are using the synchronous
+  // compositor.
+  if (!SupportsProactiveBeginFrame()) {
+    return !BeginFrameNeededToAnimateOrDraw() && ProactiveBeginFrameWanted();
+  }
+
+  // Non synchronous compositors should rely on
+  // ProactiveBeginFrameWanted to poll for state instead.
+  return false;
+}
+
+// Note: If SupportsProactiveBeginFrame is false, the scheduler should poll
+// for changes in it's draw state so it can request a BeginFrame when it's
+// actually ready.
+bool SchedulerStateMachine::SupportsProactiveBeginFrame() const {
+  // It is undesirable to proactively request BeginFrames if we are
+  // using a synchronous compositor because we *must* draw for every
+  // BeginFrame, which could cause duplicate draws.
+  return !settings_.using_synchronous_renderer_compositor;
+}
+
+void SchedulerStateMachine::SetChildrenNeedBeginFrames(
+    bool children_need_begin_frames) {
+  children_need_begin_frames_ = children_need_begin_frames;
+}
+
+void SchedulerStateMachine::SetDeferCommits(bool defer_commits) {
+  defer_commits_ = defer_commits;
+}
+
+// These are the cases where we definitely (or almost definitely) have a
+// new frame to animate and/or draw and can draw.
+bool SchedulerStateMachine::BeginFrameNeededToAnimateOrDraw() const {
+  // The forced draw respects our normal draw scheduling, so we need to
+  // request a BeginImplFrame for it.
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
+    return true;
+
+  return needs_animate_ || needs_redraw_;
+}
+
+// These are cases where we are very likely to draw soon, but might not
+// actually have a new frame to draw when we receive the next BeginImplFrame.
+// Proactively requesting the BeginImplFrame helps hide the round trip latency
+// of the SetNeedsBeginFrame request that has to go to the Browser.
+bool SchedulerStateMachine::ProactiveBeginFrameWanted() const {
+  // Do not be proactive when invisible.
+  if (!visible_)
+    return false;
+
+  // We should proactively request a BeginImplFrame if a commit is pending
+  // because we will want to draw if the commit completes quickly.
+  if (needs_commit_ || commit_state_ != COMMIT_STATE_IDLE)
+    return true;
+
+  // If the pending tree activates quickly, we'll want a BeginImplFrame soon
+  // to draw the new active tree.
+  if (has_pending_tree_)
+    return true;
+
+  // Changing priorities may allow us to activate (given the new priorities),
+  // which may result in a new frame.
+  if (needs_prepare_tiles_)
+    return true;
+
+  // If we just sent a swap request, it's likely that we are going to produce
+  // another frame soon. This helps avoid negative glitches in our
+  // SetNeedsBeginFrame requests, which may propagate to the BeginImplFrame
+  // provider and get sampled at an inopportune time, delaying the next
+  // BeginImplFrame.
+  if (request_swap_funnel_)
+    return true;
+
+  // If the last commit was aborted because of early out (no updates), we should
+  // still want a begin frame in case there is a commit coming again.
+  if (last_commit_had_no_updates_)
+    return true;
+
+  return false;
+}
+
+void SchedulerStateMachine::OnBeginImplFrame() {
+  AdvanceCurrentFrameNumber();
+  DCHECK_EQ(begin_impl_frame_state_, BEGIN_IMPL_FRAME_STATE_IDLE)
+      << AsValue()->ToString();
+  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING;
+  last_commit_had_no_updates_ = false;
+}
+
+void SchedulerStateMachine::OnBeginImplFrameDeadlinePending() {
+  DCHECK_EQ(begin_impl_frame_state_,
+            BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING)
+      << AsValue()->ToString();
+  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME;
+}
+
+void SchedulerStateMachine::OnBeginImplFrameDeadline() {
+  DCHECK_EQ(begin_impl_frame_state_, BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME)
+      << AsValue()->ToString();
+  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE;
+}
+
+void SchedulerStateMachine::OnBeginImplFrameIdle() {
+  DCHECK_EQ(begin_impl_frame_state_, BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
+      << AsValue()->ToString();
+  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_IDLE;
+}
+
+SchedulerStateMachine::BeginImplFrameDeadlineMode
+SchedulerStateMachine::CurrentBeginImplFrameDeadlineMode() const {
+  if (ShouldTriggerBeginImplFrameDeadlineImmediately()) {
+    return BEGIN_IMPL_FRAME_DEADLINE_MODE_IMMEDIATE;
+  } else if (needs_redraw_ && pending_swaps_ < max_pending_swaps_) {
+    // We have an animation or fast input path on the impl thread that wants
+    // to draw, so don't wait too long for a new active tree.
+    // If we are swap throttled we should wait until we are unblocked.
+    return BEGIN_IMPL_FRAME_DEADLINE_MODE_REGULAR;
+  } else {
+    // The impl thread doesn't have anything it wants to draw and we are just
+    // waiting for a new active tree or we are swap throttled. In short we are
+    // blocked.
+    return BEGIN_IMPL_FRAME_DEADLINE_MODE_LATE;
+  }
+}
+
+bool SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineImmediately()
+    const {
+  // TODO(brianderson): This should take into account multiple commit sources.
+
+  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME)
+    return false;
+
+  // If we've lost the output surface, end the current BeginImplFrame ASAP
+  // so we can start creating the next output surface.
+  if (output_surface_state_ == OUTPUT_SURFACE_LOST)
+    return true;
+
+  // SwapAck throttle the deadline since we wont draw and swap anyway.
+  if (pending_swaps_ >= max_pending_swaps_)
+    return false;
+
+  if (active_tree_needs_first_draw_)
+    return true;
+
+  if (!needs_redraw_)
+    return false;
+
+  // This is used to prioritize impl-thread draws when the main thread isn't
+  // producing anything, e.g., after an aborted commit. We also check that we
+  // don't have a pending tree -- otherwise we should give it a chance to
+  // activate.
+  // TODO(skyostil): Revisit this when we have more accurate deadline estimates.
+  if (commit_state_ == COMMIT_STATE_IDLE && !has_pending_tree_)
+    return true;
+
+  // Prioritize impl-thread draws in impl_latency_takes_priority_ mode.
+  if (impl_latency_takes_priority_)
+    return true;
+
+  return false;
+}
+
+bool SchedulerStateMachine::MainThreadIsInHighLatencyMode() const {
+  // If a commit is pending before the previous commit has been drawn, we
+  // are definitely in a high latency mode.
+  if (CommitPending() && (active_tree_needs_first_draw_ || has_pending_tree_))
+    return true;
+
+  // If we just sent a BeginMainFrame and haven't hit the deadline yet, the main
+  // thread is in a low latency mode.
+  if (send_begin_main_frame_funnel_ &&
+      (begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING ||
+       begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME))
+    return false;
+
+  // If there's a commit in progress it must either be from the previous frame
+  // or it started after the impl thread's deadline. In either case the main
+  // thread is in high latency mode.
+  if (CommitPending())
+    return true;
+
+  // Similarly, if there's a pending tree the main thread is in high latency
+  // mode, because either
+  //   it's from the previous frame
+  // or
+  //   we're currently drawing the active tree and the pending tree will thus
+  //   only be drawn in the next frame.
+  if (has_pending_tree_)
+    return true;
+
+  if (begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE) {
+    // Even if there's a new active tree to draw at the deadline or we've just
+    // swapped it, it may have been triggered by a previous BeginImplFrame, in
+    // which case the main thread is in a high latency mode.
+    return (active_tree_needs_first_draw_ || perform_swap_funnel_) &&
+           !send_begin_main_frame_funnel_;
+  }
+
+  // If the active tree needs its first draw in any other state, we know the
+  // main thread is in a high latency mode.
+  return active_tree_needs_first_draw_;
+}
+
+void SchedulerStateMachine::DidEnterPollForAnticipatedDrawTriggers() {
+  AdvanceCurrentFrameNumber();
+  inside_poll_for_anticipated_draw_triggers_ = true;
+}
+
+void SchedulerStateMachine::DidLeavePollForAnticipatedDrawTriggers() {
+  inside_poll_for_anticipated_draw_triggers_ = false;
+}
+
+void SchedulerStateMachine::SetVisible(bool visible) { visible_ = visible; }
+
+void SchedulerStateMachine::SetCanDraw(bool can_draw) { can_draw_ = can_draw; }
+
+void SchedulerStateMachine::SetNeedsRedraw() { needs_redraw_ = true; }
+
+void SchedulerStateMachine::SetNeedsAnimate() {
+  needs_animate_ = true;
+}
+
+void SchedulerStateMachine::SetNeedsPrepareTiles() {
+  if (!needs_prepare_tiles_) {
+    TRACE_EVENT0("cc", "SchedulerStateMachine::SetNeedsPrepareTiles");
+    needs_prepare_tiles_ = true;
+  }
+}
+
+void SchedulerStateMachine::SetMaxSwapsPending(int max) {
+  max_pending_swaps_ = max;
+}
+
+void SchedulerStateMachine::DidSwapBuffers() {
+  pending_swaps_++;
+  DCHECK_LE(pending_swaps_, max_pending_swaps_);
+  DCHECK(!perform_swap_funnel_);
+
+  perform_swap_funnel_ = true;
+  last_frame_number_swap_performed_ = current_frame_number_;
+}
+
+void SchedulerStateMachine::DidSwapBuffersComplete() {
+  DCHECK_GT(pending_swaps_, 0);
+  pending_swaps_--;
+}
+
+void SchedulerStateMachine::SetImplLatencyTakesPriority(
+    bool impl_latency_takes_priority) {
+  impl_latency_takes_priority_ = impl_latency_takes_priority;
+}
+
+void SchedulerStateMachine::DidDrawIfPossibleCompleted(DrawResult result) {
+  switch (result) {
+    case INVALID_RESULT:
+      NOTREACHED() << "Uninitialized DrawResult.";
+      break;
+    case DRAW_ABORTED_CANT_DRAW:
+    case DRAW_ABORTED_CONTEXT_LOST:
+      NOTREACHED() << "Invalid return value from DrawAndSwapIfPossible:"
+                   << result;
+      break;
+    case DRAW_SUCCESS:
+      consecutive_checkerboard_animations_ = 0;
+      forced_redraw_state_ = FORCED_REDRAW_STATE_IDLE;
+      break;
+    case DRAW_ABORTED_CHECKERBOARD_ANIMATIONS:
+      needs_redraw_ = true;
+
+      // If we're already in the middle of a redraw, we don't need to
+      // restart it.
+      if (forced_redraw_state_ != FORCED_REDRAW_STATE_IDLE)
+        return;
+
+      needs_commit_ = true;
+      consecutive_checkerboard_animations_++;
+      if (settings_.timeout_and_draw_when_animation_checkerboards &&
+          consecutive_checkerboard_animations_ >=
+              settings_.maximum_number_of_failed_draws_before_draw_is_forced_) {
+        consecutive_checkerboard_animations_ = 0;
+        // We need to force a draw, but it doesn't make sense to do this until
+        // we've committed and have new textures.
+        forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_COMMIT;
+      }
+      break;
+    case DRAW_ABORTED_MISSING_HIGH_RES_CONTENT:
+      // It's not clear whether this missing content is because of missing
+      // pictures (which requires a commit) or because of memory pressure
+      // removing textures (which might not).  To be safe, request a commit
+      // anyway.
+      needs_commit_ = true;
+      break;
+  }
+}
+
+void SchedulerStateMachine::SetNeedsCommit() {
+  needs_commit_ = true;
+}
+
+void SchedulerStateMachine::NotifyReadyToCommit() {
+  DCHECK(commit_state_ == COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED)
+      << AsValue()->ToString();
+  commit_state_ = COMMIT_STATE_READY_TO_COMMIT;
+  // In main thread low latency mode, commit should happen right after
+  // BeginFrame, meaning when this function is called, next action should be
+  // commit.
+  if (settings_.main_thread_should_always_be_low_latency)
+    DCHECK(ShouldCommit());
+}
+
+void SchedulerStateMachine::BeginMainFrameAborted(CommitEarlyOutReason reason) {
+  DCHECK_EQ(commit_state_, COMMIT_STATE_BEGIN_MAIN_FRAME_SENT);
+  switch (reason) {
+    case CommitEarlyOutReason::ABORTED_OUTPUT_SURFACE_LOST:
+    case CommitEarlyOutReason::ABORTED_NOT_VISIBLE:
+    case CommitEarlyOutReason::ABORTED_DEFERRED_COMMIT:
+      commit_state_ = COMMIT_STATE_IDLE;
+      SetNeedsCommit();
+      return;
+    case CommitEarlyOutReason::FINISHED_NO_UPDATES:
+      bool commit_has_no_updates = true;
+      UpdateStateOnCommit(commit_has_no_updates);
+      return;
+  }
+}
+
+void SchedulerStateMachine::DidPrepareTiles() {
+  needs_prepare_tiles_ = false;
+  // "Fill" the PrepareTiles funnel.
+  prepare_tiles_funnel_++;
+}
+
+void SchedulerStateMachine::DidLoseOutputSurface() {
+  if (output_surface_state_ == OUTPUT_SURFACE_LOST ||
+      output_surface_state_ == OUTPUT_SURFACE_CREATING)
+    return;
+  output_surface_state_ = OUTPUT_SURFACE_LOST;
+  needs_redraw_ = false;
+}
+
+void SchedulerStateMachine::NotifyReadyToActivate() {
+  if (has_pending_tree_)
+    pending_tree_is_ready_for_activation_ = true;
+}
+
+void SchedulerStateMachine::DidCreateAndInitializeOutputSurface() {
+  DCHECK_EQ(output_surface_state_, OUTPUT_SURFACE_CREATING);
+  output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT;
+
+  if (did_create_and_initialize_first_output_surface_) {
+    // TODO(boliu): See if we can remove this when impl-side painting is always
+    // on. Does anything on the main thread need to update after recreate?
+    needs_commit_ = true;
+  }
+  did_create_and_initialize_first_output_surface_ = true;
+  pending_swaps_ = 0;
+}
+
+void SchedulerStateMachine::NotifyBeginMainFrameStarted() {
+  DCHECK_EQ(commit_state_, COMMIT_STATE_BEGIN_MAIN_FRAME_SENT);
+  commit_state_ = COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED;
+}
+
+bool SchedulerStateMachine::HasInitializedOutputSurface() const {
+  switch (output_surface_state_) {
+    case OUTPUT_SURFACE_LOST:
+    case OUTPUT_SURFACE_CREATING:
+      return false;
+
+    case OUTPUT_SURFACE_ACTIVE:
+    case OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT:
+    case OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION:
+      return true;
+  }
+  NOTREACHED();
+  return false;
+}
+
+std::string SchedulerStateMachine::GetStatesForDebugging() const {
+  return base::StringPrintf("%c %d %d %d %c %c %c %d %d",
+      needs_commit_ ? 'T' : 'F',
+      static_cast<int>(output_surface_state_),
+      static_cast<int>(begin_impl_frame_state_),
+      static_cast<int>(commit_state_),
+      has_pending_tree_ ? 'T' : 'F',
+      pending_tree_is_ready_for_activation_ ? 'T' : 'F',
+      active_tree_needs_first_draw_ ? 'T' : 'F',
+      max_pending_swaps_,
+      pending_swaps_);
+}
+
+}  // namespace cc