Register and unregister CaptionManager listener in attach/detach

Main goal is make sure the listener is not left registered indefinitely
in Android WebView, which does not guarantee ContentViewCore.destroy to
be called.

This is probably a good change for chrome as well. Tabs in the
background should not care about caption changes. And now it no longer
registers a listener per tab, which may be a super high number.

BUG=457850, 469803

Review URL: https://codereview.chromium.org/1093353002

Cr-Commit-Position: refs/heads/master@{#326127}

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

@@ -989,7 +989,6 @@ public void destroy() {
         if (mNativeContentViewCore != 0) {
             nativeOnJavaContentViewCoreDestroyed(mNativeContentViewCore);
         }
-        mSystemCaptioningBridge.destroy();
         mWebContentsObserver.destroy();
         mWebContentsObserver = null;
         setSmartClipDataListener(null);
@@ -1506,6 +1505,7 @@ public void onAttachedToWindow() {
         restoreSelectionPopupsIfNecessary();
         ScreenOrientationListener.getInstance().addObserver(this, mContext);
         GamepadList.onAttachedToWindow(mContext);
+        mSystemCaptioningBridge.registerBridge();
     }
 
     /**
@@ -1528,6 +1528,7 @@ public void onDetachedFromWindow() {
         // locking and app switching.
         setTextHandlesTemporarilyHidden(true);
         hidePopupsAndPreserveSelection();
+        mSystemCaptioningBridge.unregisterBridge();
     }
 
     /**

content/public/android/java/src/org/chromium/content/browser/accessibility/captioning/EmptyCaptioningBridge.java

@@ -12,10 +12,18 @@ public class EmptyCaptioningBridge implements SystemCaptioningBridge {
     /**
      * A no-op implementation of the syncToDelegate function.
      */
+    @Override
     public void syncToDelegate() {}
 
     /**
-     * A no-op implementation of the destroy function.
+     * No-op implementation of registerBridge.
      */
-    public void destroy() {}
+    @Override
+    public void registerBridge() {}
+
+    /**
+     * A no-op implementation of the unregisterBridge function.
+     */
+    @Override
+    public void unregisterBridge() {}
 }

content/public/android/java/src/org/chromium/content/browser/accessibility/captioning/KitKatCaptioningBridge.java

@@ -63,13 +63,12 @@ public KitKatCaptioningBridge(ContentViewCore contenViewCore) {
         mCaptioningManager = (CaptioningManager) contenViewCore.getContext()
                                      .getApplicationContext()
                                      .getSystemService(Context.CAPTIONING_SERVICE);
-        mCaptioningManager.addCaptioningChangeListener(mCaptioningChangeListener);
-        syncToDelegate();
     }
 
     /**
      * Force-sync the current closed caption settings to the delegate
      */
+    @Override
     public void syncToDelegate() {
         mCaptioningChangeDelegate.onEnabledChanged(mCaptioningManager.isEnabled());
         mCaptioningChangeDelegate.onFontScaleChanged(mCaptioningManager.getFontScale());
@@ -79,10 +78,19 @@ public void syncToDelegate() {
     }
 
     /**
-     * De-register this bridge from the system captioning manager. This bridge
-     * should not be used again after this is called.
+     * Register this bridge for event changes with the system CaptioningManager.
+     */
+    @Override
+    public void registerBridge() {
+        mCaptioningManager.addCaptioningChangeListener(mCaptioningChangeListener);
+        syncToDelegate();
+    }
+
+    /**
+     * De-register this bridge from the system captioning manager.
      */
-    public void destroy() {
+    @Override
+    public void unregisterBridge() {
         mCaptioningManager.removeCaptioningChangeListener(mCaptioningChangeListener);
     }
 

content/public/android/java/src/org/chromium/content/browser/accessibility/captioning/SystemCaptioningBridge.java

@@ -14,8 +14,12 @@ public interface SystemCaptioningBridge {
     public void syncToDelegate();
 
     /**
-     * Removes any external listeners that were added. This implementation doesn't do anything.
-     * After destroy is called, this object should not be used again.
+     * Register this bridge for event changes with the system CaptioningManager.
      */
-    public void destroy();
+    public void registerBridge();
+
+    /**
+     * Unregister this bridge from system CaptionManager. Must be called to avoid leaks.
+     */
+    public void unregisterBridge();
 }