Buffer cross frame paint timing updates.

chrome/browser/page_load_metrics/page_load_metrics_update_dispatcher.h

Index: chrome/browser/page_load_metrics/page_load_metrics_update_dispatcher.h
diff --git a/chrome/browser/page_load_metrics/page_load_metrics_update_dispatcher.h b/chrome/browser/page_load_metrics/page_load_metrics_update_dispatcher.h
index 47f6e4f5171e0534183f852a14dad6a3af9cfc08..7af5111c47c11b938278e220db08013185f497a2 100644
--- a/chrome/browser/page_load_metrics/page_load_metrics_update_dispatcher.h
+++ b/chrome/browser/page_load_metrics/page_load_metrics_update_dispatcher.h
@@ -6,9 +6,11 @@
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_UPDATE_DISPATCHER_H_
 
 #include <map>
+#include <memory>
 
 #include "base/macros.h"
 #include "base/time/time.h"
+#include "base/timer/timer.h"
 #include "chrome/common/page_load_metrics/page_load_metrics.mojom.h"
 
 namespace content {
@@ -65,6 +67,8 @@ enum PageLoadTimingStatus {
 };
 
 extern const char kPageLoadTimingStatus[];
+extern const char kHistogramOutOfOrderTiming[];
+extern const char kHistogramOutOfOrderTimingBuffered[];
 
 }  // namespace internal
 
@@ -101,6 +105,8 @@ class PageLoadMetricsUpdateDispatcher {
   void DidFinishSubFrameNavigation(
       content::NavigationHandle* navigation_handle);
 
+  void ShutDown();
+
   const mojom::PageLoadTiming& timing() const {
     return *(current_merged_page_timing_.get());
   }
@@ -122,12 +128,7 @@ class PageLoadMetricsUpdateDispatcher {
   void UpdateMainFrameMetadata(const mojom::PageLoadMetadata& new_metadata);
   void UpdateSubFrameMetadata(const mojom::PageLoadMetadata& subframe_metadata);
 
-  // Merge values from |new_paint_timing| into |pending_merged_page_timing_|,
-  // offsetting any new timings by the |navigation_start_offset|.
-  void MergePaintTiming(base::TimeDelta navigation_start_offset,
-                        const mojom::PaintTiming& new_paint_timing,
-                        bool is_main_frame);
-
+  void MaybeDispatchTimingUpdates(bool did_merge_new_timing_value);
   void DispatchTimingUpdates();
 
   // The client is guaranteed to outlive this object.
@@ -136,6 +137,8 @@ class PageLoadMetricsUpdateDispatcher {
   // Interface to chrome features. Must outlive the class.
   PageLoadMetricsEmbedderInterface* const embedder_interface_;
 
+  std::unique_ptr<base::Timer> timer_;
+
   // Time the navigation for this page load was initiated.
   const base::TimeTicks navigation_start_;