When onPageFinished calls onNewPicture, pass null picture on SDK>=JB MR2.

android_webview/glue/java/src/com/android/webview/chromium/WebViewContentsClientAdapter.java

 // Copyright 2014 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 com.android.webview.chromium;
 
 import android.annotation.SuppressLint;
 import android.annotation.TargetApi;
 import android.content.Context;
 import android.graphics.Bitmap;
@@ skipping 82 matching lines @@
     // The Context to use. This is different from mWebView.getContext(), which should not be used.
     private final Context mContext;
     // The WebViewClient instance that was passed to WebView.setWebViewClient().
     private WebViewClient mWebViewClient = sNullWebViewClient;
     // The WebChromeClient instance that was passed to WebView.setContentViewClient().
     private WebChromeClient mWebChromeClient;
     // The listener receiving find-in-page API results.
     private WebView.FindListener mFindListener;
     // The listener receiving notifications of screen updates.
     private WebView.PictureListener mPictureListener;
+    // Whether the picture listener is invalidate only (i.e. receives a null Picture)
+    private boolean mPictureListenerInvalidateOnly;
 
     private WebViewDelegate mWebViewDelegate;
 
     private DownloadListener mDownloadListener;
 
     private Handler mUiThreadHandler;
 
     private static final int NEW_WEBVIEW_CREATED = 100;
 
     private WeakHashMap<AwPermissionRequest, WeakReference<PermissionRequestAdapter>>
@@ skipping 61 matching lines @@
     }
 
     void setDownloadListener(DownloadListener listener) {
         mDownloadListener = listener;
     }
 
     void setFindListener(WebView.FindListener listener) {
         mFindListener = listener;
     }
 
-    void setPictureListener(WebView.PictureListener listener) {
+    void setPictureListener(WebView.PictureListener listener, boolean invalidateOnly) {
         mPictureListener = listener;
+        mPictureListenerInvalidateOnly = invalidateOnly;
     }
 
     //--------------------------------------------------------------------------------------------
     //                        Adapter for all the methods.
     //--------------------------------------------------------------------------------------------
 
     /**
      * @see AwContentsClient#hasWebViewClient.
      */
     @Override
@@ skipping 346 matching lines @@
             // are invoked. The CTS harness discards any pictures it receives before
             // onPageStarted is invoked, so in the case we get the Picture before that and
             // no further updates after onPageStarted, we'll fail the test by timing
             // out waiting for a Picture.
             if (mPictureListener != null) {
                 ThreadUtils.postOnUiThreadDelayed(new Runnable() {
                     @Override
                     public void run() {
                         if (mPictureListener != null) {
                             if (TRACE) Log.d(TAG, "onPageFinished-fake");
-                            mPictureListener.onNewPicture(mWebView, new Picture());
+                            mPictureListener.onNewPicture(mWebView,
+                                    mPictureListenerInvalidateOnly ? null : new Picture());
                         }
                     }
                 }, 100);
             }
         } finally {
             TraceEvent.end("WebViewContentsClientAdapter.onPageFinished");
         }
     }
 
     /**
@@ skipping 729 matching lines @@
                 mAwPermissionRequest.deny();
             }
         }
 
         @Override
         public void deny() {
             mAwPermissionRequest.deny();
         }
     }
 }