WIP RasterCanvasLayerAllocator experiment 2

skia/ext/layer_allocator_cairo.h

Index: skia/ext/layer_allocator_cairo.h
diff --git a/skia/ext/layer_allocator_cairo.h b/skia/ext/layer_allocator_cairo.h
new file mode 100644
index 0000000000000000000000000000000000000000..8f912adb746c717ccfcfa400ba8ed7d01270ee7e
--- /dev/null
+++ b/skia/ext/layer_allocator_cairo.h
@@ -0,0 +1,47 @@
+// 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_EXT_LAYER_ALLOCATOR_CAIRO_H_
+#define SKIA_EXT_LAYER_ALLOCATOR_CAIRO_H_
+
+#include "skia/ext/platform_surface.h"
+
+#include "third_party/skia/include/core/SkRasterCanvasLayerAllocator.h"
+
+#include <unordered_map>
+
+namespace skia {
+
+/*
+ * On a stock Linux build, a PlatformCanvas is backed by a Cairo image
+ * surface; a PlatformSurface is a pointer to a Cairo context.
+ */
+class LayerAllocator : public SkRasterCanvasLayerAllocator {
+ public:
+  LayerAllocator();
+  ~LayerAllocator() override;
+
+  /// Returns cairo_t*.
+  void* getNativeContext(void* buffer,
+                         const SkMatrix& transform,
+                         const SkIRect& clip_bounds) override;
+
+ protected:
+  /// Expects a cairo_surface_t* as (optional) initialData.
+  /// Returns the data pointer from a cairo_image_surface.
+  /// |deallocator| will cairo_surface_destroy() and cairo_destroy()
+  /// the layer.
+  void* allocateLayer(const SkImageInfo& info, size_t* rowBytes,
+                      void (**deallocator)(void*),
+                      void** deallocatorPayload,
+                      void* initialData) override;
+
+ private:
+  typedef std::unordered_map<void*, cairo_t*> context_map_t;
+  context_map_t contexts_;
+};
+
+}
+
+#endif  // SKIA_EXT_LAYER_ALLOCATOR_CAIRO_H_