Add a way to extract TextureSources from a BigImageIterator. (bug 1365879 part 9, r=mattwoodrow)

gfx/layers/composite/TextureHost.h

@@ -172,6 +172,13 @@ public:
     MOZ_ASSERT(mCompositableCount >= 0);
   }
 
+  // When iterating as a BigImage, this creates temporary TextureSources wrapping
+  // individual tiles.
+  virtual RefPtr<TextureSource> ExtractCurrentTile() {
+    NS_WARNING("Implementation does not expose tile sources");
+    return nullptr;
+  }
+
   int NumCompositableRefs() const { return mCompositableCount; }
 
 protected:

gfx/layers/d3d11/TextureD3D11.cpp

@@ -1215,6 +1215,13 @@ DataTextureSourceD3D11::GetD3D11Texture() const
                     : mTexture;
 }
 
+RefPtr<TextureSource>
+DataTextureSourceD3D11::ExtractCurrentTile()
+{
+  MOZ_ASSERT(mIterating);
+  return new DataTextureSourceD3D11(mDevice, mFormat, mTileTextures[mCurrentTile]);
+}
+
 ID3D11ShaderResourceView*
 DataTextureSourceD3D11::GetShaderResourceView()
 {

gfx/layers/d3d11/TextureD3D11.h

@@ -264,6 +264,8 @@ public:
     mCurrentTile = 0;
   }
 
+  RefPtr<TextureSource> ExtractCurrentTile() override;
+
   void Reset();
 protected:
   gfx::IntRect GetTileRect(uint32_t aIndex) const;