ccpr: Unregister path listeners when their cache entries are evicted

Bug: skia:8452
Change-Id: Ibd49d8f0ed15c568156c09db358eba0415df48f5
Reviewed-on: https://skia-review.googlesource.com/c/165120
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
diff --git a/include/private/SkPathRef.h b/include/private/SkPathRef.h
index 92568d8..d250fc3 100644
--- a/include/private/SkPathRef.h
+++ b/include/private/SkPathRef.h
@@ -309,9 +309,24 @@
      */
     uint32_t genID() const;
 
-    struct GenIDChangeListener : SkRefCnt {
+    class GenIDChangeListener : public SkRefCnt {
+    public:
+        GenIDChangeListener() : fShouldUnregisterFromPath(false) {}
         virtual ~GenIDChangeListener() {}
+
         virtual void onChange() = 0;
+
+        // The caller can use this method to notify the path that it no longer needs to listen. Once
+        // called, the path will remove this listener from the list at some future point.
+        void markShouldUnregisterFromPath() {
+            fShouldUnregisterFromPath.store(true, std::memory_order_relaxed);
+        }
+        bool shouldUnregisterFromPath() {
+            return fShouldUnregisterFromPath.load(std::memory_order_acquire);
+        }
+
+    private:
+        std::atomic<bool> fShouldUnregisterFromPath;
     };
 
     void addGenIDChangeListener(sk_sp<GenIDChangeListener>);  // Threadsafe.