Use CallbackHelpers in TabStripTest

chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutTab.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutTab.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutTab.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutTab.java
index 13679ff7cc59bea4d33c7e0fe2b55724b1bbe0d0..86207a2537b58800d65557fe0692d7a7c2ad72a4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutTab.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/overlays/strip/StripLayoutTab.java
@@ -9,6 +9,7 @@ import static org.chromium.chrome.browser.compositor.layouts.ChromeAnimation.Ani
 import android.content.Context;
 import android.graphics.RectF;
 
+import org.chromium.base.ObserverList;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.compositor.layouts.ChromeAnimation;
@@ -33,6 +34,13 @@ import java.util.List;
  */
 public class StripLayoutTab
         implements ChromeAnimation.Animatable<StripLayoutTab.Property>, VirtualView {
+
+    /** An observer interface for StripLayoutTab. */
+    public interface Observer {
+        /** @param visible Whether the StripLayoutTab is visible. */
+        public void onVisibilityChanged(boolean visible);
+    }
+
     /**
      * Animatable properties that can be used with a {@link ChromeAnimation.Animatable} on a
      * {@link StripLayoutTab}.
@@ -89,6 +97,8 @@ public class StripLayoutTab
     // Preallocated
     private final RectF mClosePlacement = new RectF();
 
+    private ObserverList<Observer> mObservers = new ObserverList<>();
+
     /**
      * Create a {@link StripLayoutTab} that represents the {@link Tab} with an id of
      * {@code id}.
@@ -98,7 +108,7 @@ public class StripLayoutTab
      * @param loadTrackerCallback The {@link TabLoadTrackerCallback} to be notified of loading state
      *                            changes.
      * @param renderHost The {@link LayoutRenderHost}.
-     * @param incogntio Whether or not this layout tab is icognito.
+     * @param incognito Whether or not this layout tab is incognito.
      */
     public StripLayoutTab(Context context, int id, TabLoadTrackerCallback loadTrackerCallback,
             LayoutRenderHost renderHost, boolean incognito) {
@@ -117,6 +127,17 @@ public class StripLayoutTab
         mCloseButton.setAccessibilityDescription(description, description);
     }
 
+    /** @param observer The observer to add. */
+    @VisibleForTesting
+    public void addObserver(Observer observer) {
+        mObservers.addObserver(observer);
+    }
+
+    /** @param observer The observer to remove. */
+    public void removeObserver(Observer observer) {
+        mObservers.removeObserver(observer);
+    }
+
     /**
      * Get a list of virtual views for accessibility events.
      *
@@ -173,6 +194,9 @@ public class StripLayoutTab
      */
     public void setVisible(boolean visible) {
         mVisible = visible;
+        for (Observer observer : mObservers) {
+            observer.onVisibilityChanged(mVisible);
+        }
     }
 
     /**