Cap SkVarAlloc's desired block at 64K.

src/core/SkVarAlloc.h

 #ifndef SkVarAlloc_DEFINED
 #define SkVarAlloc_DEFINED
 
 #include "SkTypes.h"
 
 class SkVarAlloc : SkNoncopyable {
 public:
     SkVarAlloc();
     ~SkVarAlloc();
 
@@ skipping 10 matching lines @@
         fByte += bytes;
         fRemaining -= bytes;
         return ptr;
     }
 
 private:
     void makeSpace(size_t bytes, unsigned flags);
 
     char* fByte;
     unsigned fRemaining;
-    unsigned fLgMinSize;
+    unsigned fLgSize;  // This is always in the range [4, 16], so it really only needs 4 bits.
 
     struct Block;
     Block* fBlock;
 };
 
 #endif//SkVarAlloc_DEFINED