Change call-sites now that SkCanvas is not ref-counted

ui/gfx/canvas.h

Index: ui/gfx/canvas.h
diff --git a/ui/gfx/canvas.h b/ui/gfx/canvas.h
index ec85eb5374681b91ab0f1fbcfd71c1fb0ab8b0b3..521a1567f4a9835c2eb90992823fe550004a4941 100644
--- a/ui/gfx/canvas.h
+++ b/ui/gfx/canvas.h
@@ -89,7 +89,9 @@ class GFX_EXPORT Canvas {
   // Creates a Canvas backed by an |sk_canvas| with |image_scale_|.
   // |sk_canvas| is assumed to be already scaled based on |image_scale|
   // so no additional scaling is applied.
-  Canvas(sk_sp<SkCanvas> sk_canvas, float image_scale);
+  // Note: the caller must ensure that sk_canvas outlives this object, or until
+  // RecreateBackingCanvas is called.
+  Canvas(SkCanvas* sk_canvas, float image_scale);
 
   virtual ~Canvas();
 
@@ -481,7 +483,7 @@ class GFX_EXPORT Canvas {
                        const Rect& display_rect,
                        int flags);
 
-  SkCanvas* sk_canvas() { return canvas_.get(); }
+  SkCanvas* sk_canvas() { return canvas_; }
   float image_scale() const { return image_scale_; }
 
  private:
@@ -509,7 +511,12 @@ class GFX_EXPORT Canvas {
   // Canvas::Scale() does not affect |image_scale_|.
   float image_scale_;
 
-  sk_sp<SkCanvas> canvas_;
+  // canvas_ is our active canvas object. Sometimes we are also the owner,
+  // in which case canvas_owner_ will be set. Other times we are just
+  // borrowing someone else's canvas, in which case canvas_ will point there
+  // but canvas_owner_ will be null.
+  std::unique_ptr<SkCanvas> canvas_owner_;
+  SkCanvas* canvas_;
 
   DISALLOW_COPY_AND_ASSIGN(Canvas);
 };