[Herb] Add metrics to track button usage

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

Index: chrome/android/java/src/org/chromium/chrome/browser/metrics/ActivityStopMetrics.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/metrics/ActivityStopMetrics.java b/chrome/android/java/src/org/chromium/chrome/browser/metrics/ActivityStopMetrics.java
new file mode 100644
index 0000000000000000000000000000000000000000..89623f86e99b0bef048f1c01a299caaba2a8d7db
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/metrics/ActivityStopMetrics.java
@@ -0,0 +1,93 @@
+// 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.app.Activity;
+import android.support.annotation.IntDef;
+
+import org.chromium.base.ApplicationStatus;
+import org.chromium.base.metrics.RecordHistogram;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Tracks metrics caused by a particular Activity stopping.
+ */
+public class ActivityStopMetrics {
+    @Retention(RetentionPolicy.SOURCE)
+    @IntDef({
+        STOP_REASON_UNKNOWN,
+        STOP_REASON_BACK_BUTTON,
+        STOP_REASON_RETURN_BUTTON,
+        STOP_REASON_CUSTOM_TAB_STARTED,
+        STOP_REASON_CUSTOM_TAB_STOPPED,
+        STOP_REASON_OTHER_CHROME_ACTIVITY_IN_FOREGROUND,
+        STOP_REASON_COUNT
+    })
+    public @interface StopReason{}
+
+    /** Activity stopped for unknown reasons. */
+    public static final int STOP_REASON_UNKNOWN = 0;
+
+    /** Activity stopped after the user hit the back button. */
+    public static final int STOP_REASON_BACK_BUTTON = 1;
+
+    /** Activity stopped after the user hit the close/return UI button. */
+    public static final int STOP_REASON_RETURN_BUTTON = 2;
+
+    /** Activity stopped because it launched a {@link CustomTabActivity} on top of itself. */
+    public static final int STOP_REASON_CUSTOM_TAB_STARTED = 3;
+
+    /** Activity stopped because its child {@link CustomTabActivity} stopped itself. */
+    public static final int STOP_REASON_CUSTOM_TAB_STOPPED = 4;
+
+    /** Activity stopped because another of Chrome Activities came into focus. */
+    public static final int STOP_REASON_OTHER_CHROME_ACTIVITY_IN_FOREGROUND = 5;
+
+    /** Boundary.  Shouldn't ever be passed to the metrics service. */
+    public static final int STOP_REASON_COUNT = 6;
+
+    /** Name of the histogram that will be recorded. */
+    private final String mHistogramName;
+
+    /** Why the Activity is being stopped. */
+    @StopReason private int mStopReason;
+
+    /**
+     * Constructs an {@link ActivityStopMetrics} instance.
+     *
+     * @param histogramName Name to use for the histogram.

[Ilya Sherman, 2016/02/25 21:41:25]

Mmm, why did you choose to parametrize this?

[gone, 2016/02/25 22:18:14]

Just in case we want to track this kind of stat for the CustomTabActivity or
WebappActivity, as well.  Would have said it'd be useful for DocumentActivity,
but that's not going to be around much longer.

[Ilya Sherman, 2016/02/25 23:13:57]

Seems like the sort of capability that would be best to add once it's needed,
rather than as a just-in-case ahead of time.

[gone, 2016/02/25 23:29:45]

Fair enough.  I've hard-coded the histogram name for now since it's easy enough
to add in the capability later.

+     */
+    public ActivityStopMetrics(String histogramName) {
+        mHistogramName = histogramName;
+        mStopReason = STOP_REASON_COUNT;
+    }
+
+    /**
+     * Records the reason that the parent Activity was stopped.
+     * @param parent Activity that owns this {@link ActivityStopMetrics} instance.
+     */
+    public void onStopWithNative(Activity parent) {
+        if (mStopReason == STOP_REASON_COUNT) {
+            if (parent != ApplicationStatus.getLastTrackedFocusedActivity()) {
+                mStopReason = STOP_REASON_OTHER_CHROME_ACTIVITY_IN_FOREGROUND;
+            } else {
+                mStopReason = STOP_REASON_UNKNOWN;
+            }
+        }
+        RecordHistogram.recordEnumeratedHistogram(mHistogramName, mStopReason, STOP_REASON_COUNT);
+        mStopReason = STOP_REASON_COUNT;
+    }
+
+    /**
+     * Tracks the reason that the parent Activity was stopped.
+     * @param reason Reason the Activity was stopped (see {@link StopReason}).
+     */
+    public void setStopReason(@StopReason int reason) {
+        if (mStopReason != STOP_REASON_COUNT) return;
+        mStopReason = reason;
+    }
+}