Move canvas->surface association to the device subclasses

src/image/SkSurface.cpp

Index: src/image/SkSurface.cpp
diff --git a/src/image/SkSurface.cpp b/src/image/SkSurface.cpp
index 2d3fa2bf7a4eeee1e0d46943c40d45e8d73ee2b7..512a51865d36b66350192a14a09586251cdd254e 100644
--- a/src/image/SkSurface.cpp
+++ b/src/image/SkSurface.cpp
@@ -69,11 +69,6 @@ SkSurface_Base::SkSurface_Base(const SkImageInfo& info, const SkSurfaceProps* pr
 }
 
 SkSurface_Base::~SkSurface_Base() {
-    // in case the canvas outsurvives us, we null the callback
-    if (fCachedCanvas) {
-        fCachedCanvas->setSurfaceBase(NULL);
-    }
-
     SkSafeUnref(fCachedImage);
     SkSafeUnref(fCachedCanvas);
 }
@@ -89,8 +84,6 @@ void SkSurface_Base::onDraw(SkCanvas* canvas, SkScalar x, SkScalar y, const SkPa
 void SkSurface_Base::aboutToDraw(ContentChangeMode mode) {
     this->dirtyGenerationID();
 
-    SkASSERT(!fCachedCanvas || fCachedCanvas->getSurfaceBase() == this);
-
     if (fCachedImage) {
         // the surface may need to fork its backend, if its sharing it with
         // the cached image. Note: we only call if there is an outstanding owner
@@ -109,7 +102,6 @@ void SkSurface_Base::aboutToDraw(ContentChangeMode mode) {
 }
 
 uint32_t SkSurface_Base::newGenerationID() {
-    SkASSERT(!fCachedCanvas || fCachedCanvas->getSurfaceBase() == this);
     static int32_t gID;
     return sk_atomic_inc(&gID) + 1;
 }