[Android] Extract a TabModelSelectorObserver to make it more consistent.

chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorBase.java

Index: chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorBase.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorBase.java b/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorBase.java
index 47da506e292b98f617c12b084f3bea8b530ae869..3ca0c2af95247449f177b6338f654def659fcbc6 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorBase.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorBase.java
@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.tabmodel;
 
+import org.chromium.base.ObserverList;
 import org.chromium.chrome.browser.Tab;
 import org.chromium.chrome.browser.tabmodel.TabModel.TabLaunchType;
 import org.chromium.chrome.browser.tabmodel.TabModel.TabSelectionType;
@@ -21,7 +22,8 @@ public abstract class TabModelSelectorBase implements TabModelSelector {
 
     private List<TabModel> mTabModels = Collections.emptyList();
     private int mActiveModelIndex = NORMAL_TAB_MODEL_INDEX;
-    private final ArrayList<ChangeListener> mChangeListeners = new ArrayList<ChangeListener>();
+    private final ObserverList<ChangeListener> mObservers =
+            new ObserverList<ChangeListener>();
 
     protected final void initialize(boolean startIncognito, TabModel... models) {
         // Only normal and incognito supported for now.
@@ -171,13 +173,23 @@ public abstract class TabModelSelectorBase implements TabModelSelector {
     }
 
     @Override
-    public void registerChangeListener(ChangeListener changeListener) {
-        if (!mChangeListeners.contains(changeListener)) mChangeListeners.add(changeListener);
+    public void registerChangeListener(ChangeListener observer) {
+        if (!mObservers.hasObserver(observer)) mObservers.addObserver(observer);
     }
 
     @Override
-    public void unregisterChangeListener(ChangeListener changeListener) {
-        mChangeListeners.remove(changeListener);
+    public void unregisterChangeListener(ChangeListener observer) {
+        mObservers.removeObserver(observer);
+    }
+
+    @Override
+    public void addObserver(TabModelSelectorObserver observer) {
+        registerChangeListener(observer);
+    }
+
+    @Override
+    public void removeObserver(TabModelSelectorObserver observer) {
+        unregisterChangeListener(observer);
     }
 
     /**
@@ -185,8 +197,8 @@ public abstract class TabModelSelectorBase implements TabModelSelector {
      * changed.
      */
     protected void notifyChanged() {
-        for (int i = 0; i < mChangeListeners.size(); i++) {
-            mChangeListeners.get(i).onChange();
+        for (ChangeListener listener : mObservers) {
+            listener.onChange();
         }
     }
 
@@ -195,8 +207,8 @@ public abstract class TabModelSelectorBase implements TabModelSelector {
      * @param tab The tab that has been created.
      */
     private void notifyNewTabCreated(Tab tab) {
-        for (int i = 0; i < mChangeListeners.size(); i++) {
-            mChangeListeners.get(i).onNewTabCreated(tab);
+        for (ChangeListener listener : mObservers) {
+            listener.onNewTabCreated(tab);
         }
     }
 }