Plumb experiment flags through page_load_metrics and add a new observer

components/page_load_metrics/common/page_load_timing.cc

 // Copyright 2015 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 "components/page_load_metrics/common/page_load_timing.h"
+#include "third_party/WebKit/public/platform/WebExperimentData.h"
 
 namespace page_load_metrics {
 
 PageLoadTiming::PageLoadTiming() {}
 
 PageLoadTiming::PageLoadTiming(const PageLoadTiming& other) = default;
 
 PageLoadTiming::~PageLoadTiming() {}
 
 bool PageLoadTiming::operator==(const PageLoadTiming& other) const {
@@ skipping 10 matching lines @@
 }
 
 bool PageLoadTiming::IsEmpty() const {
   return navigation_start.is_null() && response_start.is_zero() &&
          dom_loading.is_zero() && dom_content_loaded_event_start.is_zero() &&
          load_event_start.is_zero() && first_layout.is_zero() &&
          first_paint.is_zero() && first_text_paint.is_zero() &&
          first_image_paint.is_zero();
 }
 
+PageLoadMetadata::PageLoadMetadata()
+    : experiment_flags(blink::WebExperimentData::NoExperiment) {}
+
+bool PageLoadMetadata::operator==(const PageLoadMetadata& other) const {
+  return experiment_flags == other.experiment_flags;
+}
+
 }  // namespace page_load_metrics