Add a UMA counter for tap disambiguation result.

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

Index: content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
index b8394ca23a122b07ceb199e6d97c1ffcb87213a3..99e952fee50398e7d6a9046c76ff09bfefc91cbe 100644
--- a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
+++ b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
@@ -1374,7 +1374,7 @@ public class ContentViewCore implements AccessibilityStateChangeListener, Displa
      */
     public boolean onKeyUp(int keyCode, KeyEvent event) {
         if (mPopupZoomer.isShowing() && keyCode == KeyEvent.KEYCODE_BACK) {
-            mPopupZoomer.hide(true);
+            mPopupZoomer.backButtonPressed();
             return true;
         }
         return mContainerViewInternals.super_onKeyUp(keyCode, event);