Add a destroy method to the TabModelSelector interface.

This will handle destroying the owned tab models, which will in turn
destroy the owned tabs.

BUG=473594

Review URL: https://codereview.chromium.org/1147153002

Cr-Commit-Position: refs/heads/master@{#330809}

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

@@ -73,7 +73,7 @@ public class SingleTabModel implements TabModel {
 
     @Override
     public int index() {
-        return 0;
+        return mTab != null ? 0 : INVALID_TAB_INDEX;
     }
 
     @Override
@@ -129,6 +129,12 @@ public class SingleTabModel implements TabModel {
         assert false;
     }
 
+    @Override
+    public void destroy() {
+        if (mTab != null) mTab.destroy();
+        mTab = null;
+    }
+
     @Override
     public Tab getNextTabIfClosed(int id) {
         return null;
@@ -175,11 +181,6 @@ public class SingleTabModel implements TabModel {
         mObservers.removeObserver(observer);
     }
 
-    // Below are functions that are overridden but should be moved out of TabModel.
-    @Override
-    public void destroy() {
-    }
-
     private static native void nativePermanentlyBlockAllNewWindows(Tab nativeTabAndroid);
 
 }

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

@@ -140,6 +140,9 @@ public interface TabModel extends TabList {
     /**
      * To be called when this model should be destroyed.  The model should no longer be used after
      * this.
+     *
+     * <p>
+     * As a result of this call, all {@link Tab}s owned by this model should be destroyed.
      */
     public void destroy();
 

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

@@ -158,4 +158,9 @@ public interface TabModelSelector {
      * @return Whether the tab state for this {@link TabModelSelector} has been initialized.
      */
     boolean isTabStateInitialized();
+
+    /**
+     * Destroy all owned {@link TabModel}s and {@link Tab}s referenced by this selector.
+     */
+    void destroy();
 }

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

@@ -207,6 +207,11 @@ public abstract class TabModelSelectorBase implements TabModelSelector {
         return mTabStateInitialized;
     }
 
+    @Override
+    public void destroy() {
+        for (int i = 0; i < getModels().size(); i++) getModelAt(i).destroy();
+    }
+
     /**
      * Notifies all the listeners that the {@link TabModelSelector} or its {@link TabModel} has
      * changed.