cc cleanup: Remove an unused field.

CompositorFrameReportingController::stage_history_ is never used, so
it is removed.

BUG=none
R=behdadb@chromium.org

Change-Id: I27a40a306c7a55d871900ec4fbcc64196ffbc454
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2129236
Auto-Submit: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Reviewed-by: Behdad Bakhshinategh <behdadb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754932}

cc/metrics/compositor_frame_reporting_controller.h

@@ -9,8 +9,6 @@
 #include <vector>
 
 #include "base/time/time.h"
-#include "cc/base/base_export.h"
-#include "cc/base/rolling_time_delta_history.h"
 #include "cc/cc_export.h"
 #include "cc/metrics/compositor_frame_reporter.h"
 #include "cc/metrics/event_metrics.h"
@@ -22,7 +20,6 @@ struct FrameTimingDetails;
 
 namespace cc {
 struct BeginMainFrameMetrics;
-class RollingTimeDeltaHistory;
 
 // This is used for managing simultaneous CompositorFrameReporter instances
 // in the case that the compositor has high latency. Calling one of the
@@ -107,22 +104,14 @@ class CC_EXPORT CompositorFrameReportingController {
   // The latency reporter passed to each CompositorFrameReporter. Owned here
   // because it must be common among all reporters.
   // DO NOT reorder this line and the ones below. The latency_ukm_reporter_ must
-  // outlive the objects in stage_history_ and submitted_compositor_frames_.
+  // outlive the objects in |submitted_compositor_frames_|.
   std::unique_ptr<LatencyUkmReporter> latency_ukm_reporter_;
 
   // Mapping of frame token to pipeline reporter for submitted compositor
   // frames.
   // DO NOT reorder this line and the one above. The latency_ukm_reporter_ must
-  // outlive the objects in stage_history_ and submitted_compositor_frames_.
+  // outlive the objects in |submitted_compositor_frames_|.
   base::circular_deque<SubmittedCompositorFrame> submitted_compositor_frames_;
-
-  // These keep track of stage durations for when a frame did not miss a
-  // deadline. The history is used by reporter instances to determine if a
-  // missed frame had a stage duration that was abnormally large.
-  // DO NOT reorder this line and the ones above. The latency_ukm_reporter_ must
-  // outlive the objects in stage_history_ and submitted_compositor_frames_.
-  std::unique_ptr<RollingTimeDeltaHistory> stage_history_[static_cast<size_t>(
-      CompositorFrameReporter::StageType::kStageTypeCount)];
 };
 }  // namespace cc