Make SharedMemory track the size that was actually mapped

ui/surface/transport_dib.cc

+// Copyright (c) 2013 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 "ui/surface/transport_dib.h"
+
+#include "skia/ext/platform_canvas.h"
+
+// static
+bool TransportDIB::VerifyCanvasSize(int w, int h) {
+  static const size_t kMaxSize = static_cast<size_t>(INT_MAX);
+  const size_t one_stride = skia::PlatformCanvasStrideForWidth(1);
+  const size_t stride = skia::PlatformCanvasStrideForWidth(w);
+  if (w <= 0 || h <= 0 || static_cast<size_t>(w) > (kMaxSize / one_stride) ||
+      static_cast<size_t>(h) > (kMaxSize / stride)) {
+    return false;
+  }
+
+  return (stride * h) <= size_;
+}
+