Do not register onLayoutListener unless it is needed

isKeyboardShowing calls getWindowVisibleDisplayFrame which may be very
expensive sine it involves ipc to other processes. Also layout happens a
lot more often in webview than chrome, so this disproportionately
affects webview.

BUG=487487

Review URL: https://codereview.chromium.org/1140163004

Cr-Commit-Position: refs/heads/master@{#329973}

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

@@ -51,12 +51,25 @@ public class ActivityWindowAndroid
     public ActivityWindowAndroid(Activity activity, boolean listenToActivityState) {
         super(activity.getApplicationContext());
         mActivityRef = new WeakReference<Activity>(activity);
-        activity.findViewById(android.R.id.content).addOnLayoutChangeListener(this);
         if (listenToActivityState) {
             ApplicationStatus.registerStateListenerForActivity(this, activity);
         }
     }
 
+    @Override
+    protected void registerKeyboardVisibilityCallbacks() {
+        Activity activity = mActivityRef.get();
+        if (activity == null) return;
+        activity.findViewById(android.R.id.content).addOnLayoutChangeListener(this);
+    }
+
+    @Override
+    protected void unregisterKeyboardVisibilityCallbacks() {
+        Activity activity = mActivityRef.get();
+        if (activity == null) return;
+        activity.findViewById(android.R.id.content).removeOnLayoutChangeListener(this);
+    }
+
     @Override
     public int showCancelableIntent(
             PendingIntent intent, IntentCallback callback, Integer errorId) {

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

@@ -405,11 +405,20 @@ public class WindowAndroid {
         return mKeyboardAccessoryView;
     }
 
+    protected void registerKeyboardVisibilityCallbacks() {
+    }
+
+    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();
+        }
     }
 
     /**