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..2db54bf86909a7d063fd65a1e6ec4218025a4326 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 GlyphHashTraits {

[mtklein, 2015/07/21 19:35:52]

Seems fine, but now that you're scoped here, HashTraits is just as clear, maybe
clearer.

[herb_g, 2015/07/21 22:27:34]

Done.

+    public:
+        static uint32_t GetKey(const SkGlyph& glyph) {
+            return glyph.fID;
+        }
+        static uint32_t Hash(uint32_t glyphId) {
+            return SkChecksum::CheapMix(glyphId);

[mtklein, 2015/07/21 19:35:52]

If we're seeing a lot of time spent looking through the hash table, that may
also indicate we have a poor hash function.  I am skeptical of the quality of
CheapMix().  Might try Mix().

[herb_g, 2015/07/21 22:27:34]

I think I'm going to work on tuning the hashing table in another cl.

[mtklein, 2015/07/21 22:30:30]

Oh, yeah, most definitely another CL.  SGTM!

+        }
+    };
+
  private:
     // TODO(herb) remove friend statement after SkGlyphCache cleanup.
     friend class SkGlyphCache;