Plumb experiment flags through page_load_metrics and add a new observer

components/page_load_metrics/renderer/page_timing_metrics_sender.cc

Index: components/page_load_metrics/renderer/page_timing_metrics_sender.cc
diff --git a/components/page_load_metrics/renderer/page_timing_metrics_sender.cc b/components/page_load_metrics/renderer/page_timing_metrics_sender.cc
index 52d87704aa3ee2ed79f2be6d7ff2acddf4f2e967..cb8dd7015de8caf3c32182808d562222fa076117 100644
--- a/components/page_load_metrics/renderer/page_timing_metrics_sender.cc
+++ b/components/page_load_metrics/renderer/page_timing_metrics_sender.cc
@@ -23,7 +23,8 @@ PageTimingMetricsSender::PageTimingMetricsSender(IPC::Sender* ipc_sender,
                                                  scoped_ptr<base::Timer> timer)
     : ipc_sender_(ipc_sender),
       routing_id_(routing_id),
-      timer_(std::move(timer)) {}
+      timer_(std::move(timer)),
+      metadata_(PageLoadMetadata()) {}
 
 // On destruction, we want to send any data we have if we have a timer
 // currently running (and thus are talking to a browser process)
@@ -34,6 +35,10 @@ PageTimingMetricsSender::~PageTimingMetricsSender() {
   }
 }
 
+void PageTimingMetricsSender::DidUseExperiment(blink::WebExperimentData data) {
+  metadata_.experiment_flags |= data;
+}
+
 void PageTimingMetricsSender::Send(const PageLoadTiming& timing) {
   if (timing == last_timing_)
     return;
@@ -55,8 +60,8 @@ void PageTimingMetricsSender::Send(const PageLoadTiming& timing) {
 }
 
 void PageTimingMetricsSender::SendNow() {
-  ipc_sender_->Send(
-      new PageLoadMetricsMsg_TimingUpdated(routing_id_, last_timing_));
+  ipc_sender_->Send(new PageLoadMetricsMsg_TimingUpdated(
+      routing_id_, last_timing_, metadata_));
 }
 
 }  // namespace page_load_metrics