[NoStatePrefetch] Add performance histograms.

chrome/browser/page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..955734d724ce29d1e5158a121ef47eef9ba5e2b4
--- /dev/null
+++ b/chrome/browser/page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h
@@ -0,0 +1,46 @@
+// Copyright 2016 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.
+
+#ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_NO_STATE_PREFETCH_PAGE_LOAD_METRICS_OBSERVER_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_NO_STATE_PREFETCH_PAGE_LOAD_METRICS_OBSERVER_H_
+
+#include "base/macros.h"
+#include "chrome/browser/page_load_metrics/page_load_metrics_observer.h"
+#include "url/gurl.h"
+
+namespace content {
+class WebContents;
+}
+
+namespace prerender {
+class PrerenderManager;
+}
+
+// Observer recording metrics related to NoStatePrefetch.
+class NoStatePrefetchPageLoadMetricsObserver
+    : public page_load_metrics::PageLoadMetricsObserver {
+ public:
+  // Returns a NoStatePrefetchPageLoadMetricsObserver, or nullptr if it is not
+  // needed.
+  static std::unique_ptr<NoStatePrefetchPageLoadMetricsObserver> CreateIfNeeded(
+      content::WebContents* web_contents);
+
+  explicit NoStatePrefetchPageLoadMetricsObserver(
+      prerender::PrerenderManager* manager);
+  ~NoStatePrefetchPageLoadMetricsObserver() override;
+
+ private:
+  // page_load_metrics::PageLoadMetricsObserver overrides:

[Charlie Harrison, 2016/09/19 16:40:06]

nit: remove "overrides"

+  void OnCommit(content::NavigationHandle* navigation_handle) override;
+  void OnFirstContentfulPaint(
+      const page_load_metrics::PageLoadTiming& timing,
+      const page_load_metrics::PageLoadExtraInfo& extra_info) override;
+
+  bool is_no_store_;  // True if the main resource has a "no-store" HTTP header.
+  prerender::PrerenderManager* const prerender_manager_;
+
+  DISALLOW_COPY_AND_ASSIGN(NoStatePrefetchPageLoadMetricsObserver);
+};
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_NO_STATE_PREFETCH_PAGE_LOAD_METRICS_OBSERVER_H_