cc: Fix flaky LayerTreeHostScrollTestImplSideInvalidation

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"
@@ skipping 675 matching lines @@
   DCHECK(!send_begin_main_frame_funnel_);
   begin_main_frame_state_ = BEGIN_MAIN_FRAME_STATE_SENT;
   needs_begin_main_frame_ = false;
   send_begin_main_frame_funnel_ = true;
   last_frame_number_begin_main_frame_sent_ = current_frame_number_;
   last_begin_frame_sequence_number_begin_main_frame_sent_ =
       begin_frame_sequence_number_;
 }
 
 void SchedulerStateMachine::WillCommit(bool commit_has_no_updates) {
-  DCHECK(!has_pending_tree_ ||
-         (settings_.main_frame_before_activation_enabled &&
-          commit_has_no_updates));
+  bool can_have_pending_tree =
+      commit_has_no_updates &&
+      (settings_.main_frame_before_activation_enabled ||
+       current_pending_tree_is_impl_side_);
+  DCHECK(!has_pending_tree_ || can_have_pending_tree);
   commit_count_++;
   last_commit_had_no_updates_ = commit_has_no_updates;
   begin_main_frame_state_ = BEGIN_MAIN_FRAME_STATE_IDLE;
 
   if (commit_has_no_updates) {
     // Pending tree might still exist from prior commit.
     if (has_pending_tree_) {
-      DCHECK(settings_.main_frame_before_activation_enabled);
+      DCHECK(can_have_pending_tree);
       last_begin_frame_sequence_number_pending_tree_was_fresh_ =
           last_begin_frame_sequence_number_begin_main_frame_sent_;
     } else {
       if (last_begin_frame_sequence_number_compositor_frame_was_fresh_ ==
           last_begin_frame_sequence_number_active_tree_was_fresh_) {
         // Assuming that SetNeedsRedraw() is only called at the beginning of
         // a BeginFrame, we can update the compositor frame freshness.
         last_begin_frame_sequence_number_compositor_frame_was_fresh_ =
             last_begin_frame_sequence_number_begin_main_frame_sent_;
       }
@@ skipping 616 matching lines @@
     case COMPOSITOR_FRAME_SINK_ACTIVE:
     case COMPOSITOR_FRAME_SINK_WAITING_FOR_FIRST_COMMIT:
     case COMPOSITOR_FRAME_SINK_WAITING_FOR_FIRST_ACTIVATION:
       return true;
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace cc