SkTDynamicHash: pick up GetKey(), Hash() from T by default.

src/core/SkTDynamicHash.h

Index: src/core/SkTDynamicHash.h
diff --git a/src/core/SkTDynamicHash.h b/src/core/SkTDynamicHash.h
index 0e34270e0b459765f705405e85106706c48a9a9d..c9a0b3ed01cfaa24cb3851f8fe9cd5c2125af2dd 100644
--- a/src/core/SkTDynamicHash.h
+++ b/src/core/SkTDynamicHash.h
@@ -12,10 +12,13 @@
 #include "SkTemplates.h"
 #include "SkTypes.h"
 
+// Traits requires:
+//   static const Key& GetKey(const T&) { ... }
+//   static uint32_t Hash(const Key&) { ... }
+// We'll look on T for these by default, or you can pass a custom Traits type.
 template <typename T,
           typename Key,
-          const Key& (GetKey)(const T&),
-          uint32_t (Hash)(const Key&),
+          typename Traits = T,
           int kGrowPercent = 75>  // Larger -> more memory efficient, but slower.
 class SkTDynamicHash {
 public:
@@ -227,6 +230,9 @@ private:
         return (index + round + 1) & this->hashMask();
     }
 
+    static const Key& GetKey(const T& t) { return Traits::GetKey(t); }
+    static uint32_t Hash(const Key& key) { return Traits::Hash(key); }
+
     int fCount;     // Number of non Empty(), non Deleted() entries in fArray.
     int fDeleted;   // Number of Deleted() entries in fArray.
     int fCapacity;  // Number of entries in fArray.  Always a power of 2.