Add SkBitmap StructTraits for skia::mojo::Bitmap.

skia/public/interfaces/bitmap_skbitmap_struct_traits.h

+// Copyright 2016 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.
+
+#ifndef SKIA_PUBLIC_INTERFACES_BITMAP_SKBITMAP_STRUCT_TRAITS_H_
+#define SKIA_PUBLIC_INTERFACES_BITMAP_SKBITMAP_STRUCT_TRAITS_H_
+
+#include "mojo/public/cpp/bindings/array_traits.h"
+#include "skia/public/interfaces/bitmap.mojom.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace mojo {
+
+// A buffer used to read pixel data directly from BitmapDataView to SkBitmap.
+struct BitmapBuffer {
+  uint8_t* data = nullptr;
+  size_t size = 0;
+};
+
+// ArrayTraits needed for ReadPixelData use with BitmapBuffer.
+template <>
+struct ArrayTraits<BitmapBuffer> {
+  using Element = uint8_t;
+  static bool IsNull(const BitmapBuffer& b);
+  static void SetToNull(BitmapBuffer* b);
+  static size_t GetSize(const BitmapBuffer& b);
+  static uint8_t* GetData(BitmapBuffer& b);
+  static const uint8_t* GetData(const BitmapBuffer& b);
+  static uint8_t& GetAt(BitmapBuffer& b, size_t i);
+  static const uint8_t& GetAt(const BitmapBuffer& b, size_t i);
+  static void Resize(BitmapBuffer& b, size_t size);
+};
+
+// Struct traits to use SkBitmap for skia::mojom::Bitmap in Chrome C++ code.
+template <>
+struct StructTraits<skia::mojom::Bitmap, SkBitmap> {
+  static skia::mojom::ColorType color_type(const SkBitmap& r);

[yzshen1, 2016/05/31 23:17:36]

I had a previous comment about adding IsNull and SetToNull to this StructTraits.

Otherwise, the current usage in image decoder of sending a nullable bitmap will
break.

[msw, 2016/05/31 23:53:41]

Done. Sorry I somehow neglected that! Though, I wonder if that interface
actually needs a nullable bitmap now... image_decoder_impl.cc instead returns a
default-constructed SkBitmap, and the client, image_decoder.cc, checks the
returned bitmap's isNull() function for valid pixels (isNull()==true for a
default-constructed SkBitmap). Since the only impl/client is in C++ and SkBitmap
has isNull(), we could probably remove the struct traits IsNull/SetToNull, and
make image_decoder.mojom always return an SkBitmap. WDYT?

+  static skia::mojom::AlphaType alpha_type(const SkBitmap& r);
+  static skia::mojom::ColorProfileType profile_type(const SkBitmap& r);
+  static uint32_t width(const SkBitmap& r);
+  static uint32_t height(const SkBitmap& r);
+  static BitmapBuffer pixel_data(const SkBitmap& r);
+  static bool Read(skia::mojom::BitmapDataView data, SkBitmap* out);
+  static void* SetUpContext(const SkBitmap& r);
+  static void TearDownContext(const SkBitmap& r, void* context);
+};
+
+}  // namespace mojo
+
+#endif  // SKIA_PUBLIC_INTERFACES_BITMAP_SKBITMAP_STRUCT_TRAITS_H_