Fix behavior of sk_sp::reset() and add unittest.

tests/RefCntTest.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRefCnt.h"
 #include "SkThreadUtils.h"
 #include "SkTypes.h"
@@ skipping 272 matching lines @@
 };
 }
 static sk_sp<FooAbstract> make_foo() {
     // can not cast FooConcrete to FooAbstract.
     // can cast FooConcrete* to FooAbstract*.
     return sk_make_sp<FooConcrete>();
 }
 DEF_TEST(sk_make_sp, r) {
     auto x = make_foo();
 }
+
+// Test that reset() "adopts" ownership from the caller, even if we are given the same ptr twice
+//
+DEF_TEST(sk_sp_reset, r) {
+    SkRefCnt* rc = new SkRefCnt;
+    REPORTER_ASSERT(r, 1 == rc->unique());

[bungeman-skia, 2016/03/06 14:01:44]

This reads a little funny with the unexpected thinking about the 1 converting to
bool, this should either just be 'rc->unique()' (and below ('!rc->unique()'
instead of '2 == rc->getRefCnt()) or it should be '1 == rc->getRefCnt()'.

[reed1, 2016/03/06 19:03:43]

Done.

+
+    sk_sp<SkRefCnt> sp;
+    sp.reset(rc);
+    // We have transfered our ownership over to sp
+    REPORTER_ASSERT(r, 1 == rc->unique());
+
+    rc->ref();  // now "rc" is also an owner
+#ifdef SK_DEBUG
+    REPORTER_ASSERT(r, 2 == rc->getRefCnt());
+#endif
+
+    sp.reset(rc);   // this should transfer our ownership over to sp
+    REPORTER_ASSERT(r, 1 == rc->unique());
+}