cc: Don't leak a ref to SkColorFilter.

skia/ext/refptr.h

Index: skia/ext/refptr.h
diff --git a/skia/ext/refptr.h b/skia/ext/refptr.h
index a3900f61ba4502c0d59c3b8664cf6bb4dd3c4aa1..5d3165988ae6ace57c4fb393ad8cc84f6da933ee 100644
--- a/skia/ext/refptr.h
+++ b/skia/ext/refptr.h
@@ -5,6 +5,8 @@
 #ifndef SKIA_EXT_REFPTR_H_
 #define SKIA_EXT_REFPTR_H_
 
+#include "base/basictypes.h"
+#include "base/logging.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 
 namespace skia {
@@ -87,6 +89,41 @@ class RefPtr {
     return ptr_ ? &RefPtr::ptr_ : NULL;
   }
 
+  class Receiver {
+   public:
+    ~Receiver() {
+      DCHECK(!*refptr_) << "RefPtr must be empty.";
+      refptr_->ptr_ = ptr_;
+    }
+
+    operator T**() { return &ptr_; }
+
+   private:
+    friend class RefPtr;
+
+    explicit Receiver(RefPtr* refptr) : refptr_(refptr), ptr_(NULL) {
+      DCHECK(!*refptr_) << "RefPtr must be empty.";
+    }
+
+    RefPtr* refptr_;
+    T* ptr_;
+
+    DISALLOW_COPY_AND_ASSIGN(Receiver);
+  };
+
+  // Call this and pass it to a function that takes a T** argument and
+  // sets it to an object with an unowned reference.

[awong, 2013/07/17 23:51:02]

suggestion:
Call this and pass the returned temporary to a function taking a T** argument.
The returned temporary will set the original RefPtr to an object with an unowned
reference.

+  // NOTE: Do not use this function as part of a subexpression, and try to use

[awong, 2013/07/17 23:51:02]

suggestion:
Do not use this function as part of a subexpression where the RefPtr is also
used somewhere else. Destructors of temporaries are only run at the end of a
full expression so the initialization will not be complete and the RefPtr will
remain empty.

[danakj, 2013/07/17 23:58:29]

Thanks, will do.

I think that I can also DCHECK this to guarantee safety (tho it requires adding
a bool RefPtr and adding DCHECK to a lot of places, so I think only in debug
builds would be appropriate).

+  // the RefPtr in the same subexpression, as this operation will not be
+  // complete and the RefPtr will be empty still.
+  //
+  // Bad (refptr will be NULL when it is dereffed):
+  //   Foo(refptr.ReceiveAndAdoptRef()) && refptr->Bar();
+  // Good:
+  //   bool ok = Foo(refptr.ReceiveAndAdoptRef());
+  //   ok && refptr->Bar();
+  Receiver ReceiveAndAdoptRef() { return Receiver(this); }
+
  private:
   T* ptr_;