Bug 804852: Support for the hwc implementation of Composer2D. r=mattwoodrow,mwu,roc sr=roc

This is a rollup of the following patches

part 0: Add a dynamic cast to ColorLayer*

part 1: Add a Composer2D interface to enable implementations to more efficiently compose layer trees

part 2: Let widgets expose Composer2Ds, if they have them

part 3: Expose a layers ogl "friend" API that Composer2D will consume

part 4: Hook Composer2D into the LayerManagerOGL rendering pipeline

part 5: Implement all the goop to let widget/gonk use a Composer2D (HwcComposer2D)

gfx/layers/opengl/Composer2D.h

@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=8 et :
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_Composer2D_h
+#define mozilla_layers_Composer2D_h
+
+#include "gfxTypes.h"
+#include "nsISupportsImpl.h"
+
+/**
+ * Many platforms have dedicated hardware for simple composition.
+ * This hardware is usually faster or more power efficient than the
+ * GPU.  However, in exchange for this better performance, generality
+ * has to be sacrificed: no 3d transforms, no intermediate surfaces,
+ * no special shader effects, loss of other goodies depending on the
+ * platform.
+ *
+ * Composer2D is a very simple interface to this class of hardware
+ * that allows an implementation to "try rendering" with the fast
+ * path.  If the given layer tree requires more generality than the
+ * hardware provides, the implementation should bail and have the
+ * layer manager fall back on full GPU composition.
+ */
+
+class gfxMatrix;
+
+namespace mozilla {
+namespace layers {
+
+class Layer;
+
+class THEBES_API Composer2D {
+  NS_INLINE_DECL_REFCOUNTING(Composer2D)
+
+public:
+  virtual ~Composer2D() {}
+
+  /**
+   * Return true if |aRoot| met the implementation's criteria for fast
+   * composition and the render was successful.  Return false to fall
+   * back on the GPU.
+   *
+   * |aWorldTransform| must be applied to |aRoot|'s subtree when
+   * rendering to the framebuffer.  This is a global transform on the
+   * entire scene, defined in GL space.  If the Composer2D
+   * implementation is unable to honor the transform, it should return
+   * false.
+   *
+   * Currently, when TryRender() returns true, the entire framebuffer
+   * must have been rendered.
+   */
+  virtual bool TryRender(Layer* aRoot, const gfxMatrix& aWorldTransform) = 0;
+};
+
+} // namespace layers
+} // namespace mozilla
+
+#endif // mozilla_layers_Composer2D_h