[MediaNotification] Add UMA to record user clicking media notifications

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

Index: chrome/android/java/src/org/chromium/chrome/browser/metrics/LaunchFromNotificationUMA.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/metrics/LaunchFromNotificationUMA.java b/chrome/android/java/src/org/chromium/chrome/browser/metrics/LaunchFromNotificationUMA.java
new file mode 100644
index 0000000000000000000000000000000000000000..6c141e0c49cbdfac478f907648ae299836b07895
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/metrics/LaunchFromNotificationUMA.java
@@ -0,0 +1,36 @@
+// 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 android.content.Intent;
+
+/**
+ * Helper class to record which kind of notifications does the user click to go back to Chrome.
+ */
+public class LaunchFromNotificationUMA {

[gone, 2016/04/20 22:17:14]

LaunchFromNotificationUma, not UMA.  media/ uniquely breaks the naming
convention when it shouldn't.

[Zhiqiang Zhang (Slow), 2016/04/21 16:36:53]

Done.

+    public static final int SOURCE_INVALID = -1;
+    public static final int SOURCE_MEDIA = 0;
+    public static final int SOURCE_PRESENTATION = 1;
+    public static final int SOURCE_MEDIA_FLING = 2;
+    public static final int SOURCE_MAX = 3;
+
+    public static final String INTENT_EXTRA_NAME = "Launch.NotificationSource";

[gone, 2016/04/20 22:17:14]

This doesn't have to match the histogram name.  All Intent extras should be
prefaced with the package name so that we don't get conflicts.

Use something like this instead:
public static final String EXTRA_NOTIFICATION_SOURCE =
"org.chromium.chrome.browser.metrics.LaunchFromNotificationUMA.NOTIFICATION_SOURCE";

[Zhiqiang Zhang (Slow), 2016/04/21 16:36:52]

Done.

+
+    private static final LaunchMetrics

[gone, 2016/04/20 22:17:14]

Formatting is super wacky here.  can you import
LaunchMetrics.EnumeratedHistogramSample instead?

[Zhiqiang Zhang (Slow), 2016/04/21 16:36:53]

Done.

+            .EnumeratedHistogramSample sNotificationLaunchSourceHistogram =
+            new LaunchMetrics.EnumeratedHistogramSample("Launch.NotificationSource", SOURCE_MAX);
+
+    /**
+     * Record the UMA as specified by {@link intent}. The {@link intent} should contain intent extra
+     * of name {@link INTENT_EXTRA_NAME} indicating the type.
+     * @param intent The intent starting the activity.
+     */
+    public static void recordSource(Intent intent) {
+        if (intent == null) return;
+        int source = intent.getIntExtra(INTENT_EXTRA_NAME, SOURCE_INVALID);
+        if (source == SOURCE_INVALID) return;

[gone, 2016/04/20 22:17:14]

if (source <= SOURCE_INVALID || source >= SOURCE_MAX)

[Zhiqiang Zhang (Slow), 2016/04/21 16:36:52]

Done.

+        sNotificationLaunchSourceHistogram.record(source);
+    }
+}