Pass the quad's rect (contents_rect) origin to skia image filters as an offset in the CTM.

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index e35b6975f1ea79f457e87f76229dea64e9414fed..62122c812d2fd9ff4a75355947a9fb61e9065340 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -513,6 +513,7 @@ static inline SkBitmap ApplyFilters(GLRenderer* renderer,
 
 static SkBitmap ApplyImageFilter(GLRenderer* renderer,
                                  ContextProvider* offscreen_contexts,
+                                 gfx::Point origin,
                                  SkImageFilter* filter,
                                  ScopedResource* source_texture_resource) {
   if (!filter)
@@ -577,6 +578,7 @@ static SkBitmap ApplyImageFilter(GLRenderer* renderer,
   SkPaint paint;
   paint.setImageFilter(filter);
   canvas.clear(SK_ColorTRANSPARENT);
+  canvas.translate(SkIntToScalar(-origin.x()), SkIntToScalar(-origin.y()));

[danakj, 2013/08/29 02:07:16]

Can you add a TODO here stating that the filter should be scaled by the scale
from the layer space of the root-most layer drawn into the render pass draw
quad's texture (ie. the surface owning texture), to the render pass draw quad's
texture? And point to a crbug where we will do this?

[Stephen White, 2013/08/29 17:07:00]

Done.

   canvas.drawSprite(source, 0, 0, &paint);
 
   // Flush skia context so that all the rendered stuff appears on the
@@ -778,6 +780,7 @@ void GLRenderer::DrawRenderPassQuad(DrawingFrame* frame,
     } else {
       filter_bitmap = ApplyImageFilter(this,
                                        frame->offscreen_context_provider,
+                                       quad->rect.origin(),
                                        quad->filter.get(),
                                        contents_texture);
     }