Add a UMA counter for tap disambiguation result.

content/public/android/java/src/org/chromium/content/browser/PopupZoomer.java

Index: content/public/android/java/src/org/chromium/content/browser/PopupZoomer.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/PopupZoomer.java b/content/public/android/java/src/org/chromium/content/browser/PopupZoomer.java
index bec4df581dd348df7631b23d3a57e622c6c2f034..1dfe8f3685e4c5655e76d64c0885f31730445f87 100644
--- a/content/public/android/java/src/org/chromium/content/browser/PopupZoomer.java
+++ b/content/public/android/java/src/org/chromium/content/browser/PopupZoomer.java
@@ -30,11 +30,14 @@ import android.view.animation.OvershootInterpolator;
 
 import org.chromium.base.ApiCompatibilityUtils;
 import org.chromium.base.Log;
+import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.content.R;
 
 /**
- * PopupZoomer is used to show the on-demand link zooming popup. It handles manipulation of the
- * canvas and touch events to display the on-demand zoom magnifier.
+ * PopupZoomer is used to show the tap disambiguation popup.  When a tap lands ambiguously
+ * between two tiny touch targets (usually links) on a desktop site viewed on a phone,
+ * a magnified view of the content is shown, the screen is grayed out and the user
+ * must re-tap the magnified content in order to clarify their intent.
  */
 class PopupZoomer extends View {
     private static final String TAG = "cr.PopupZoomer";
@@ -46,6 +49,15 @@ class PopupZoomer extends View {
     // Time it takes for the animation to finish in ms.
     private static final long ANIMATION_DURATION = 300;
 
+    // Note that these values should be cross-checked against
+    // tools/metrics/histograms/histograms.xml.

[Ilya Sherman, 2017/03/24 22:16:56]

Please also document that, since it is used to back an UMA histogram, the enum
should be treated as append-only.

[aelias_OOO_until_Jul13, 2017/03/24 22:30:31]

Done.

+    private static final String UMA_TAPDISAMBIGUATION = "PopupZoomer.TapDisambiguation";
+    private static final int UMA_TAPDISAMBIGUATION_TAPPEDINSIDE = 0;
+    private static final int UMA_TAPDISAMBIGUATION_TAPPEDOUTSIDE = 1;

[Ilya Sherman, 2017/03/24 22:16:56]

nit: Why do you not have underscores between "TAP" and "DISAMBIGUATION" and
between "TAPPED" and "OUTSIDE"?

[aelias_OOO_until_Jul13, 2017/03/24 22:30:31]

I prefer to use the underscore as a category separator (type vs value) rather
than as a word separator.

+    private static final int UMA_TAPDISAMBIGUATION_BACKBUTTON = 2;
+    private static final int UMA_TAPDISAMBIGUATION_OTHER = 3;
+    private static final int UMA_TAPDISAMBIGUATION_COUNT = 4;
+
     /**
      * Interface to be implemented to listen for touch events inside the zoomed area.
      * The MotionEvent coordinates correspond to original unzoomed view.
@@ -188,7 +200,7 @@ class PopupZoomer extends View {
                         if (mAnimating) return true;
 
                         if (isTouchOutsideArea(e1.getX(), e1.getY())) {
-                            hide(true);
+                            tappedOutside();
                         } else {
                             scroll(distanceX, distanceY);
                         }
@@ -211,8 +223,7 @@ class PopupZoomer extends View {
                         float x = e.getX();
                         float y = e.getY();
                         if (isTouchOutsideArea(x, y)) {
-                            // User clicked on area outside the popup.
-                            hide(true);
+                            tappedOutside();
                         } else if (mOnTapListener != null) {
                             PointF converted = convertTouchPoint(x, y);
                             MotionEvent event = MotionEvent.obtainNoHistory(e);
@@ -222,7 +233,7 @@ class PopupZoomer extends View {
                             } else {
                                 mOnTapListener.onSingleTap(PopupZoomer.this, event);
                             }
-                            hide(true);
+                            tappedInside();
                         }
                         return true;
                     }
@@ -509,18 +520,46 @@ class PopupZoomer extends View {
     }
 
     /**
-     * Hide the PopupZoomer view.
+     * Hide the PopupZoomer view because of some external event such as focus
+     * change, JS-originating scroll, etc.
      * @param animation true if hide with animation.
      */
     public void hide(boolean animation) {
         if (!mShowing) return;
 
+        RecordHistogram.recordEnumeratedHistogram(
+                UMA_TAPDISAMBIGUATION, UMA_TAPDISAMBIGUATION_OTHER, UMA_TAPDISAMBIGUATION_COUNT);
+
         if (animation) {
             startAnimation(false);
         } else {
             hideImmediately();
         }
     }
+    private void tappedInside() {
+        if (!mShowing) return;
+        RecordHistogram.recordEnumeratedHistogram(UMA_TAPDISAMBIGUATION,
+                UMA_TAPDISAMBIGUATION_TAPPEDINSIDE, UMA_TAPDISAMBIGUATION_COUNT);
+
+        startAnimation(false);
+    }
+
+    private void tappedOutside() {
+        if (!mShowing) return;
+        RecordHistogram.recordEnumeratedHistogram(UMA_TAPDISAMBIGUATION,
+                UMA_TAPDISAMBIGUATION_TAPPEDOUTSIDE, UMA_TAPDISAMBIGUATION_COUNT);

[Ilya Sherman, 2017/03/24 22:16:57]

nit: It's generally a best-practice to have one call-site per histogram, i.e. to
create a small wrapper function.  In Java, this mostly just reduces the chances
of code path drift.  (In C++, there are also some binary size improvements; not
sure whether those apply to Java to some extent as well.)

[aelias_OOO_until_Jul13, 2017/03/24 22:30:31]

Done.

+
+        startAnimation(false);
+    }
+
+    public void backButtonPressed() {
+        if (!mShowing) return;
+
+        RecordHistogram.recordEnumeratedHistogram(UMA_TAPDISAMBIGUATION,
+                UMA_TAPDISAMBIGUATION_BACKBUTTON, UMA_TAPDISAMBIGUATION_COUNT);
+
+        startAnimation(false);
+    }
 
     /**
      * Converts the coordinates to a point on the original un-zoomed view.