customtabs: Send time to first contentful paint to the caller.

chrome/browser/page_load_metrics/observers/android_page_load_metrics_observer.h

+// 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_ANDROID_PAGE_LOAD_METRICS_OBSERVER_H_
+#define CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_ANDROID_PAGE_LOAD_METRICS_OBSERVER_H_
+
+#include <jni.h>
+
+#include "base/macros.h"
+#include "components/page_load_metrics/browser/page_load_metrics_observer.h"
+
+namespace content {
+class WebContents;
+}  // namespace content
+
+class GURL;
+
+/** Forwards page load metrics to the Java side on Android. */
+class AndroidPageLoadMetricsObserver
+    : public page_load_metrics::PageLoadMetricsObserver {
+ public:
+  AndroidPageLoadMetricsObserver(content::WebContents* web_contents);
+
+  // page_load_metrics::PageLoadMetricsObserver:
+  void OnTimingUpdate(

[Bryan McQuade, 2016/07/21 23:56:13]

we added a new OnFirstContentfulPaint which gets called zero or one times, when
a FCP happens. can you use that instead? OTOH maybe we just want to push the
whole PageLoadTiming struct over to the java side every time it gets updated, in
which case implementing OnTimingUpdate is the right thing to do.

[Benoit L, 2016/07/22 15:41:31]

Let's start with a simple callback first, using OnFirstContentfulPaint() as you
suggested. On the Android side though, I think we want to keep the interface
generic, since the public-facing API is only updatable when new versions of the
Android support library ship.

+      const page_load_metrics::PageLoadTiming& timing,
+      const page_load_metrics::PageLoadExtraInfo& extra_info) override;
+
+ private:
+  content::WebContents* web_contents_;
+  bool has_seen_first_contentful_paint_;
+
+  DISALLOW_COPY_AND_ASSIGN(AndroidPageLoadMetricsObserver);
+};
+
+bool RegisterPageLoadMetricsBindings(JNIEnv* env);
+
+#endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_ANDROID_PAGE_LOAD_METRICS_OBSERVER_H_