use murmur3 finisher to improve font hash efficiency

src/core/SkGlyphCache.h

Index: src/core/SkGlyphCache.h
diff --git a/src/core/SkGlyphCache.h b/src/core/SkGlyphCache.h
index bb34a7d977411784971c9658793ad787e7197237..e11a46025e1d7d5223f348ab04a4929b5069c57a 100644
--- a/src/core/SkGlyphCache.h
+++ b/src/core/SkGlyphCache.h
@@ -1,4 +1,3 @@
-
 /*
  * Copyright 2006 The Android Open Source Project
  *
@@ -6,11 +5,11 @@
  * found in the LICENSE file.
  */
 
-
 #ifndef SkGlyphCache_DEFINED
 #define SkGlyphCache_DEFINED
 
 #include "SkBitmap.h"
+#include "SkChecksum.h"
 #include "SkChunkAlloc.h"
 #include "SkDescriptor.h"
 #include "SkGlyph.h"
@@ -23,6 +22,10 @@ class SkPaint;
 
 class SkGlyphCache_Globals;
 
+// Enable this locally to add stats for hash-table hit rates. It also extends the dump()
+// output to show those stats.
+//#define SK_GLYPHCACHE_TRACK_HASH_STATS
+
 /** \class SkGlyphCache
 
     This class represents a strike: a specific combination of typeface, size,
@@ -101,6 +104,8 @@ public:
         return fScalerContext->isSubpixel();
     }
 
+    void dump() const;
+
     /*  AuxProc/Data allow a client to associate data with this cache entry.
         Multiple clients can use this, as their data is keyed with a function
         pointer. In addition to serving as a key, the function pointer is called
@@ -145,6 +150,8 @@ public:
         return VisitCache(typeface, desc, DetachProc, NULL);
     }
 
+    static void Dump();
+
 #ifdef SK_DEBUG
     void validate() const;
 #else
@@ -204,15 +211,19 @@ private:
     // no reason to use the same kHashCount as fGlyphHash, but we do for now
     CharGlyphRec    fCharToGlyphHash[kHashCount];
 
-    static inline unsigned ID2HashIndex(uint32_t id) {
-        id ^= id >> 16;
-        id ^= id >> 8;
-        return id & kHashMask;
+    static inline unsigned ID2HashIndex(uint32_t h) {
+        return SkChecksum::CheapMix(h) & kHashMask;
     }
 
     // used to track (approx) how much ram is tied-up in this cache
     size_t  fMemoryUsed;
 
+
+#ifdef SK_GLYPHCACHE_TRACK_HASH_STATS
+    int fHashHitCount;
+    int fHashMissCount;
+#endif
+
     struct AuxProcRec {
         AuxProcRec* fNext;
         void (*fProc)(void*);