Do not register onLayoutListener unless it is needed

ui/android/java/src/org/chromium/ui/base/WindowAndroid.java

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.ui.base;
 
 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.annotation.SuppressLint;
 import android.annotation.TargetApi;
@@ skipping 387 matching lines @@
         mKeyboardAccessoryView = view;
     }
 
     /**
      * {@see setKeyboardAccessoryView(ViewGroup)}.
      */
     public ViewGroup getKeyboardAccessoryView() {
         return mKeyboardAccessoryView;
     }
 
+    protected void registerKeyboardVisibilityCallbacks() {

[jdduke (slow), 2015/05/14 21:51:54]

Should we be failing here, or just asserting false or something like that?
Adding keyboard listeners for anything but ActivityWindowAndroid doesn't make
any sense.

[boliu, 2015/05/14 23:05:29]

I don't want to add random asserts that I don't actually is holds or not, this
close to the branch point..

[jdduke (slow), 2015/05/14 23:09:36]

How is it random? In what world should we be registering listeners when it turns
out that the listener won't ever be honored?

[boliu, 2015/05/14 23:12:47]

Random as in it's not part of this fix (and I don't want to do the work to
verify the assert holds :p ).

Fix is safer if it doesn't add new assumptions.

+    }
+
+    protected void unregisterKeyboardVisibilityCallbacks() {
+    }
+
     /**
      * Adds a listener that is updated of keyboard visibility changes. This works as a best guess.
      * {@see UiUtils.isKeyboardShowing}
      */
     public void addKeyboardVisibilityListener(KeyboardVisibilityListener listener) {
+        if (mKeyboardVisibilityListeners.isEmpty()) {
+            registerKeyboardVisibilityCallbacks();
+        }
         mKeyboardVisibilityListeners.add(listener);
     }
 
     /**
      * {@see addKeyboardVisibilityListener()}.
      */
     public void removeKeyboardVisibilityListener(KeyboardVisibilityListener listener) {
         mKeyboardVisibilityListeners.remove(listener);
+        if (mKeyboardVisibilityListeners.isEmpty()) {
+            unregisterKeyboardVisibilityCallbacks();
+        }
     }
 
     /**
      * To be called when the keyboard visibility state might have changed. Informs listeners of the
      * state change IFF there actually was a change.
      * @param isShowing The current (guesstimated) state of the keyboard.
      */
     protected void keyboardVisibilityPossiblyChanged(boolean isShowing) {
         if (mIsKeyboardShowing == isShowing) return;
         mIsKeyboardShowing = isShowing;
@@ skipping 57 matching lines @@
 
     private native long nativeInit();
     private native void nativeOnVSync(long nativeWindowAndroid,
                                       long vsyncTimeMicros,
                                       long vsyncPeriodMicros);
     private native void nativeOnActivityPaused(long nativeWindowAndroid);
     private native void nativeOnActivityResumed(long nativeWindowAndroid);
     private native void nativeDestroy(long nativeWindowAndroid);
 
 }