Add a 'unique' method to SkRefCnt, document the usage, and add support.

src/core/SkPathRef.h

Index: src/core/SkPathRef.h
===================================================================
--- src/core/SkPathRef.h	(revision 10052)
+++ src/core/SkPathRef.h	(working copy)
@@ -37,15 +37,16 @@
     public:
         Editor(SkAutoTUnref<SkPathRef>* pathRef,
                int incReserveVerbs = 0,
-               int incReservePoints = 0) {
-            if (pathRef->get()->getRefCnt() > 1) {
+               int incReservePoints = 0)
+        {
+            if ((*pathRef)->unique()) {
+                (*pathRef)->incReserve(incReserveVerbs, incReservePoints);

[Dmitry Vyukov, 2013/07/16 15:26:23]

Won't it be modified after this unique() check?

[bungeman-skia, 2013/07/16 15:50:57]

Yes, but it will only be modified when unique returns or would return true. The
entire reason for this check is copy on write (and no copy is needed ~99% of the
time) to avoid the heavy overhead of 'new' below. Because this is copy on write
(only modify when you're the only owner) there are no modifications on other
threads to the owned object which need to happen before using the owned object.

+            } else {
                 SkPathRef* copy = SkNEW(SkPathRef);
-                copy->copy(*pathRef->get(), incReserveVerbs, incReservePoints);
+                copy->copy(**pathRef, incReserveVerbs, incReservePoints);
                 pathRef->reset(copy);
-            } else {
-                (*pathRef)->incReserve(incReserveVerbs, incReservePoints);
             }
-            fPathRef = pathRef->get();
+            fPathRef = *pathRef;
             fPathRef->fGenerationID = 0;
             SkDEBUGCODE(sk_atomic_inc(&fPathRef->fEditorsAttached);)
         }
@@ -135,18 +136,18 @@
                                       const SkMatrix& matrix) {
         src.validate();
         if (matrix.isIdentity()) {
-            if (dst->get() != &src) {
+            if (*dst != &src) {
                 src.ref();
                 dst->reset(const_cast<SkPathRef*>(&src));
                 (*dst)->validate();
             }
             return;
         }
-        int32_t rcnt = dst->get()->getRefCnt();
-        if (&src == dst->get() && 1 == rcnt) {
+        bool dstUnique = (*dst)->unique();
+        if (&src == *dst && dstUnique) {
             matrix.mapPoints((*dst)->fPoints, (*dst)->fPointCnt);
             return;
-        } else if (rcnt > 1) {
+        } else if (!dstUnique) {
             dst->reset(SkNEW(SkPathRef));
         }
         (*dst)->resetToSize(src.fVerbCnt, src.fPointCnt, src.fConicWeights.count());
@@ -179,7 +180,7 @@
      * only if necessary.
      */
     static void Rewind(SkAutoTUnref<SkPathRef>* pathRef) {
-        if (1 == (*pathRef)->getRefCnt()) {
+        if ((*pathRef)->unique()) {
             (*pathRef)->validate();
             (*pathRef)->fVerbCnt = 0;
             (*pathRef)->fPointCnt = 0;