Avoid null-pointer dereference for PPAPI Instance BindGraphics....

webkit/plugins/ppapi/ppapi_plugin_instance.cc

 // Copyright (c) 2010 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.
 
 #include "webkit/plugins/ppapi/ppapi_plugin_instance.h"
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/scoped_ptr.h"
 #include "base/utf_string_conversions.h"
@@ skipping 442 matching lines @@
     if (!graphics_2d->BindToInstance(this))
       return false;  // Can't bind to more than one instance.
 
     // See http://crbug.com/49403: this can be further optimized by keeping the
     // old device around and painting from it.
     if (bound_graphics_2d()) {
       // Start the new image with the content of the old image until the plugin
       // repaints.
       const SkBitmap* old_backing_bitmap =
           bound_graphics_2d()->image_data()->GetMappedBitmap();
-      SkRect old_size = SkRect::MakeWH(
-          SkScalar(static_cast<float>(old_backing_bitmap->width())),
-          SkScalar(static_cast<float>(old_backing_bitmap->height())));
+      if (old_backing_bitmap != NULL) {

[neb, 2011/01/24 21:32:21]

Shouldn't it fail if NULL? That should not be possible short of internal error
or malicious code.

+        SkRect old_size = SkRect::MakeWH(
+            SkScalar(static_cast<float>(old_backing_bitmap->width())),
+            SkScalar(static_cast<float>(old_backing_bitmap->height())));
 
-      SkCanvas canvas(*graphics_2d->image_data()->GetMappedBitmap());
-      canvas.drawBitmap(*old_backing_bitmap, 0, 0);
+        SkCanvas canvas(*graphics_2d->image_data()->GetMappedBitmap());
+        canvas.drawBitmap(*old_backing_bitmap, 0, 0);
 
-      // Fill in any extra space with white.
-      canvas.clipRect(old_size, SkRegion::kDifference_Op);
-      canvas.drawARGB(255, 255, 255, 255);
+        // Fill in any extra space with white.
+        canvas.clipRect(old_size, SkRegion::kDifference_Op);
+        canvas.drawARGB(255, 255, 255, 255);
+      }
     }
 
     bound_graphics_ = graphics_2d;
     // BindToInstance will have invalidated the plugin if necessary.
   } else if (graphics_3d) {
     // Make sure graphics can only be bound to the instance it is
     // associated with.
     if (graphics_3d->instance() != this)
       return false;
     if (!graphics_3d->BindToInstance(true))
@@ skipping 747 matching lines @@
   return found->second;
 }
 
 bool PluginInstance::IsFullPagePlugin() const {
   WebFrame* frame = container()->element().document().frame();
   return frame->view()->mainFrame()->document().isPluginDocument();
 }
 
 }  // namespace ppapi
 }  // namespace webkit