SkPictureRecord: silently do nothing for non-drawable SkBitmaps.

include/core/SkBitmap.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBitmap_DEFINED
 #define SkBitmap_DEFINED
 
@@ skipping 62 matching lines @@
     /** Copies the src bitmap into this bitmap. Ownership of the src bitmap's pixels remains
         with the src bitmap.
     */
     SkBitmap& operator=(const SkBitmap& src);
     /** Swap the fields of the two bitmaps. This routine is guaranteed to never fail or throw.
     */
     //  This method is not exported to java.
     void swap(SkBitmap& other);
 
     /** Return true iff the bitmap has empty dimensions.
-    */
+     *  Hey!  Before you use this, see if you really want to know drawsNothing() instead.
+     */
     bool empty() const { return 0 == fWidth || 0 == fHeight; }
 
     /** Return true iff the bitmap has no pixelref. Note: this can return true even if the
-        dimensions of the bitmap are > 0 (see empty()).
-    */
+     *  dimensions of the bitmap are > 0 (see empty()).
+     *  Hey!  Before you use this, see if you really want to know drawsNothing() instead.
+     */
     bool isNull() const { return NULL == fPixelRef; }
 
+    /** Return true iff drawing this bitmap has no effect.
+     */
+    bool drawsNothing() const { return this->empty() || this->isNull(); }
+
     /** Return the config for the bitmap. */
     Config  config() const { return (Config)fConfig; }
 
     SK_ATTR_DEPRECATED("use config()")
     Config  getConfig() const { return this->config(); }
 
     /** Return the bitmap's width, in pixels. */
     int width() const { return fWidth; }
 
     /** Return the bitmap's height, in pixels. */
@@ skipping 774 matching lines @@
 
 inline SkPMColor SkBitmap::getIndex8Color(int x, int y) const {
     SkASSERT(fPixels);
     SkASSERT(fConfig == kIndex8_Config);
     SkASSERT((unsigned)x < fWidth && (unsigned)y < fHeight);
     SkASSERT(fColorTable);
     return (*fColorTable)[*((const uint8_t*)fPixels + y * fRowBytes + x)];
 }
 
 #endif