Android: Remove an unused API from ContentViewCore

|ContentViewCore.isAttachedToWindow| became unused after a series
of refactoring. This CL removes the interface and implementation.

Bug: 598880
Change-Id: Ic1cbb747b50230e8851143b01524cd75ba156a9b
Reviewed-on: https://chromium-review.googlesource.com/979390Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545997}

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

@@ -407,11 +407,6 @@ public class ContentViewCoreImpl implements ContentViewCore, DisplayAndroidObser
         nativeResetGestureDetection(mNativeContentViewCore);
     }
 
-    @Override
-    public boolean isAttachedToWindow() {
-        return mAttachedToWindow;
-    }
-
     @SuppressWarnings("javadoc")
     @Override
     public void onAttachedToWindow() {

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

@@ -159,11 +159,6 @@ public interface ContentViewCore {
      */
     void onHide();
 
-    /**
-     * Whether or not the associated ContentView is currently attached to a window.
-     */
-    boolean isAttachedToWindow();
-
     /**
      * @see View#onAttachedToWindow()
      */

content/public/test/android/javatests/src/org/chromium/content/browser/test/util/TestContentViewCore.java

@@ -55,11 +55,6 @@ public class TestContentViewCore implements ContentViewCore {
     @Override
     public void onHide() {}
 
-    @Override
-    public boolean isAttachedToWindow() {
-        return false;
-    }
-
     @Override
     public void onAttachedToWindow() {}