test_shell: fix for newer cairos

skia/ext/bitmap_platform_device_linux.cc

 // Copyright (c) 2009 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 "skia/ext/bitmap_platform_device_linux.h"
 
 #include <cairo/cairo.h>
 
 namespace skia {
 
@@ skipping 169 matching lines @@
     const BitmapPlatformDevice& other)
     : PlatformDevice(const_cast<BitmapPlatformDevice&>(
                           other).accessBitmap(true)),
       data_(other.data_) {
 }
 
 BitmapPlatformDevice::~BitmapPlatformDevice() {
 }
 
 cairo_t* BitmapPlatformDevice::beginPlatformPaint() {
-  return data_->GetContext();
+  cairo_t* cairo = data_->GetContext();
+  // Tell Cairo that we've (probably) modified its pixel buffer without
+  // its knowledge.
+  cairo_surface_mark_dirty(cairo_get_target(cairo));
+  return cairo;
 }
 
 void BitmapPlatformDevice::setMatrixClip(const SkMatrix& transform,
                                          const SkRegion& region) {
   data_->SetMatrixClip(transform, region);
 }
 
 BitmapPlatformDevice& BitmapPlatformDevice::operator=(
     const BitmapPlatformDevice& other) {
   data_ = other.data_;
   return *this;
 }
 
 }  // namespace skia