Fix fading overlay events

chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
index ada13e59355e35342b6a580943661830b0720926..a186f8746a97f51605c1c50b95f4a9a92d1cab05 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
@@ -151,7 +151,9 @@ import org.chromium.ui.base.PageTransition;
 import org.chromium.ui.base.WindowAndroid;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 import javax.annotation.Nullable;
@@ -254,7 +256,7 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
 
     // A set of views obscuring all tabs. When this set is nonempty,
     // all tab content will be hidden from the accessibility tree.
-    private List<View> mViewsObscuringAllTabs = new ArrayList<>();
+    private Set<View> mViewsObscuringAllTabs = new HashSet<>();
 
     // See enableHardwareAcceleration()
     private boolean mSetWindowHWA;