Base SkAutoTUnref on skstd::unique_ptr.

To further consolidate the various unique owning classes, this bases
SkAutoTUnref on skstd::unique_ptr. Users are updated because of two
breaking changes, swap now takes a reference and reset no longer
returns its argument.

Review URL: https://codereview.chromium.org/1370803002
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index 97e3438..1326362 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -180,7 +180,7 @@
 
 void SkPath::swap(SkPath& that) {
     if (this != &that) {
-        fPathRef.swap(&that.fPathRef);
+        fPathRef.swap(that.fPathRef);
         SkTSwap<int>(fLastMoveToIndex, that.fLastMoveToIndex);
         SkTSwap<uint8_t>(fFillType, that.fFillType);
         SkTSwap<uint8_t>(fConvexity, that.fConvexity);