[cc] Calculate the correct latest_confirmed_sequence_number in cc::Scheduler.

cc/scheduler/scheduler_state_machine.h

Index: cc/scheduler/scheduler_state_machine.h
diff --git a/cc/scheduler/scheduler_state_machine.h b/cc/scheduler/scheduler_state_machine.h
index 975c32e097d7a54fca6d167c107ea1cc1a470872..2ad99993d683fa73be950a2eab41b1937fbdc4dd 100644
--- a/cc/scheduler/scheduler_state_machine.h
+++ b/cc/scheduler/scheduler_state_machine.h
@@ -5,12 +5,13 @@
 #ifndef CC_SCHEDULER_SCHEDULER_STATE_MACHINE_H_
 #define CC_SCHEDULER_SCHEDULER_STATE_MACHINE_H_
 
+#include <stdint.h>
+
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
-#include "cc/output/begin_frame_args.h"
 #include "cc/scheduler/commit_earlyout_reason.h"
 #include "cc/scheduler/draw_result.h"
 #include "cc/scheduler/scheduler_settings.h"
@@ -146,10 +147,16 @@ class CC_EXPORT SchedulerStateMachine {
   // to make progress.
   bool BeginFrameNeeded() const;
 
+  // Indicates that the Scheduler has received a BeginFrame that did not require
+  // a BeginImplFrame, because the Scheduler stopped observing BeginFrames.
+  // Updates the sequence and freshness numbers for the dropped BeginFrame.
+  void OnBeginFrameDroppedNotObserving(uint32_t source_id,
+                                       uint64_t sequence_number);
+
   // Indicates that the system has entered and left a BeginImplFrame callback.
   // The scheduler will not draw more than once in a given BeginImplFrame
   // callback nor send more than one BeginMainFrame message.
-  void OnBeginImplFrame();
+  void OnBeginImplFrame(uint32_t source_id, uint64_t sequence_number);
   // Indicates that the scheduler has entered the draw phase. The scheduler
   // will not draw more than once in a single draw phase.
   // TODO(sunnyps): Rename OnBeginImplFrameDeadline to OnDraw or similar.
@@ -282,6 +289,11 @@ class CC_EXPORT SchedulerStateMachine {
     return previous_pending_tree_was_impl_side_;
   }
 
+  uint32_t begin_frame_source_id() const { return begin_frame_source_id_; }
+  uint64_t last_begin_frame_sequence_number_compositor_frame_was_fresh() const {
+    return last_begin_frame_sequence_number_compositor_frame_was_fresh_;
+  }
+
  protected:
   bool BeginFrameRequiredForAction() const;
   bool BeginFrameNeededForVideo() const;
@@ -308,6 +320,10 @@ class CC_EXPORT SchedulerStateMachine {
   void WillPerformImplSideInvalidationInternal();
   void DidDrawInternal(DrawResult draw_result);
 
+  void UpdateBeginFrameSequenceNumbersForBeginFrame(uint32_t source_id,
+                                                    uint64_t sequence_number);
+  void UpdateBeginFrameSequenceNumbersForBeginFrameDeadline();
+
   const SchedulerSettings settings_;
 
   CompositorFrameSinkState compositor_frame_sink_state_;
@@ -315,6 +331,17 @@ class CC_EXPORT SchedulerStateMachine {
   BeginMainFrameState begin_main_frame_state_;
   ForcedRedrawOnTimeoutState forced_redraw_state_;
 
+  // These fields are used to track the freshness of pending updates in the
+  // commit/activate/draw pipeline. The Scheduler uses the CompositorFrame's
+  // freshness to fill the |latest_confirmed_sequence_number| field in
+  // BeginFrameAcks.
+  uint32_t begin_frame_source_id_;
+  uint64_t begin_frame_sequence_number_;
+  uint64_t last_begin_frame_sequence_number_begin_main_frame_sent_;
+  uint64_t last_begin_frame_sequence_number_pending_tree_was_fresh_;
+  uint64_t last_begin_frame_sequence_number_active_tree_was_fresh_;
+  uint64_t last_begin_frame_sequence_number_compositor_frame_was_fresh_;
+
   // These are used for tracing only.
   int commit_count_;
   int current_frame_number_;