Do not register onLayoutListener unless it is needed

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

Index: ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
diff --git a/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java b/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
index c14de9eaff86c85679a5b602adc1d03ce46f7254..84a34990d35a0c5df5375c3de7a071557f31fdac 100644
--- a/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
+++ b/ui/android/java/src/org/chromium/ui/base/WindowAndroid.java
@@ -405,11 +405,20 @@ public class WindowAndroid {
         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);
     }
 
@@ -418,6 +427,9 @@ public class WindowAndroid {
      */
     public void removeKeyboardVisibilityListener(KeyboardVisibilityListener listener) {
         mKeyboardVisibilityListeners.remove(listener);
+        if (mKeyboardVisibilityListeners.isEmpty()) {
+            unregisterKeyboardVisibilityCallbacks();
+        }
     }
 
     /**