Plumb experiment flags through page_load_metrics and add a new observer

chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc

Index: chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc
diff --git a/chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc b/chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc
index 88aeb9479d1af9e743097ac5c0a0e5df90e49148..3b99e35bac738848a1f359ba48ab5a64b503af91 100644
--- a/chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc
+++ b/chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc
@@ -100,10 +100,19 @@ void PageLoadMetricsObserverTestHarness::StartNavigation(const GURL& gurl) {
 void PageLoadMetricsObserverTestHarness::SimulateTimingUpdate(
     const PageLoadTiming& timing) {
   observer_->OnMessageReceived(

[Bryan McQuade, 2016/04/11 20:18:47]

can this method call the new SimulateTimingAndMetadataUpdate with an empty
PageLoadMetadata?

[Charlie Harrison, 2016/04/12 15:18:50]

Done.

-      PageLoadMetricsMsg_TimingUpdated(observer_->routing_id(), timing),
+      PageLoadMetricsMsg_TimingUpdated(observer_->routing_id(), timing,
+                                       PageLoadMetadata()),
       web_contents()->GetMainFrame());
 }
 
+void PageLoadMetricsObserverTestHarness::SimulateTimingAndMetadataUpdate(
+    const PageLoadTiming& timing,
+    const PageLoadMetadata& metadata) {
+  observer_->OnMessageReceived(PageLoadMetricsMsg_TimingUpdated(
+                                   observer_->routing_id(), timing, metadata),
+                               web_contents()->GetMainFrame());
+}
+
 const base::HistogramTester&
 PageLoadMetricsObserverTestHarness::histogram_tester() const {
   return histogram_tester_;