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

tests/RefCntTest.cpp

Index: tests/RefCntTest.cpp
diff --git a/tests/RefCntTest.cpp b/tests/RefCntTest.cpp
index 8914ccff49a092fc2ca8d337cf80a1f9090fb15a..f9be9e80ba51ba12e8be652c861b8c876b3bfcca 100644
--- a/tests/RefCntTest.cpp
+++ b/tests/RefCntTest.cpp
@@ -290,3 +290,23 @@ static sk_sp<FooAbstract> make_foo() {
 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());
+}