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

chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java

Index: chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java b/chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java
new file mode 100644
index 0000000000000000000000000000000000000000..fcec2286467627894b9c39f5f206880ac166aa61
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java
@@ -0,0 +1,58 @@
+// 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.
+
+package org.chromium.chrome.browser.metrics;
+
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.content_public.browser.WebContents;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Receives the page load metrics updates from AndroidPageLoadMetricsObserver, and notifies the
+ * observers.
+ *
+ * Threading: everything here must happen on the UI thread.
+ */
+public class PageLoadMetrics {
+    /** Observer for page load metrics. */
+    public interface Observer {
+        /**
+         * Called when the first contentful paint page load metric is available.
+         *
+         * @param webContents the WebContents this metrics is related to.
+         * @param firstContentfulPaintMs Time to first contentful paint from navigation start.
+         */
+        public void onFirstContentfulPaintMetricUpdate(
+                WebContents webContents, double firstContentfulPaintMs);
+    }
+
+    private static List<Observer> sObservers = null;
+
+    /** Adds an observer. */
+    public static void addObserver(Observer observer) {
+        ThreadUtils.assertOnUiThread();
+        if (sObservers == null) sObservers = new ArrayList<Observer>();
+        sObservers.add(observer);
+    }
+
+    /** Removes an observer. */
+    public static void removeObserver(Observer observer) {
+        ThreadUtils.assertOnUiThread();
+        sObservers.remove(observer);
+        if (sObservers.size() == 0) sObservers = null;
+    }
+
+    @CalledByNative
+    static void onFirstContentfulPaintMetricUpdate(
+            WebContents webContents, double firstContentfulPaintMs) {
+        ThreadUtils.assertOnUiThread();
+        if (sObservers == null) return;
+        for (Observer observer : sObservers) {
+            observer.onFirstContentfulPaintMetricUpdate(webContents, firstContentfulPaintMs);
+        }
+    }
+}