Move the GlyphCache to use a hash table instead of doing its own ad-hoc

src/core/SkGlyph.h

Index: src/core/SkGlyph.h
diff --git a/src/core/SkGlyph.h b/src/core/SkGlyph.h
index abca215d0039510da7218fcf031770901967e186..469985959cc867d825d31810a57556bb13c2da3f 100644
--- a/src/core/SkGlyph.h
+++ b/src/core/SkGlyph.h
@@ -8,6 +8,7 @@
 #ifndef SkGlyph_DEFINED
 #define SkGlyph_DEFINED
 
+#include "SkChecksum.h"
 #include "SkTypes.h"
 #include "SkFixed.h"
 #include "SkMask.h"
@@ -114,6 +115,16 @@ class SkGlyph {
 
     void toMask(SkMask* mask) const;
 
+    class HashTraits {
+    public:
+        static uint32_t GetKey(const SkGlyph& glyph) {
+            return glyph.fID;
+        }
+        static uint32_t Hash(uint32_t glyphId) {
+            return SkChecksum::CheapMix(glyphId);
+        }
+    };
+
  private:
     // TODO(herb) remove friend statement after SkGlyphCache cleanup.
     friend class SkGlyphCache;