Switch to one-at-a-time SkPicture::clone interface

cc/resources/picture.cc

Index: cc/resources/picture.cc
diff --git a/cc/resources/picture.cc b/cc/resources/picture.cc
index a19fd33f3a0724906b5fad324c0bd7d3a5fc28ee..5244ec9aa0b391c313d97113a2c7f0209439abed 100644
--- a/cc/resources/picture.cc
+++ b/cc/resources/picture.cc
@@ -231,15 +231,12 @@ void Picture::CloneForDrawing(int num_threads) {
   raster_thread_checker_.DetachFromThread();
 
   if (num_threads > 1) {
-    scoped_ptr<SkPicture[]> clones(new SkPicture[num_threads - 1]);
+    scoped_ptr<SkPicture* []> clones(new SkPicture* [num_threads - 1]);

[danakj, 2014/07/10 19:57:05]

This is an array of raw SkRefCnt pointers? Since skia won't adopt something like
skia::RefPtr I don't know what to suggest given this intended skia api. I just
wanted to say that this makes me super sad, cuz we can't immediately wrap the
raw pointers in RefPtr like this.

If this was more common I'd suggest a RefPtrVector similar to
ScopedPtrVector.....

[mtklein, 2014/07/10 20:09:51]

Why don't we rewrite this to just use the other existing clone method,
  SkPicture* SkPicture::clone() const;
?

This still lets us remove the default constructor and the copy constructor, and
allows Picture to wrap the SkPicture* in a skia::AdoptRef right away.

This means we also don't have to land the Skia-side CL adding void
SkPicture::clone(SkPicture* [], int).

     picture_->clone(&clones[0], num_threads - 1);
 
     for (int i = 0; i < num_threads - 1; i++) {
-      scoped_refptr<Picture> clone = make_scoped_refptr(
-          new Picture(skia::AdoptRef(new SkPicture(clones[i])),
-                      layer_rect_,
-                      opaque_rect_,
-                      pixel_refs_));
+      scoped_refptr<Picture> clone = make_scoped_refptr(new Picture(
+          skia::AdoptRef(clones[i]), layer_rect_, opaque_rect_, pixel_refs_));
       clones_.push_back(clone);
 
       clone->EmitTraceSnapshotAlias(this);