Reduce the size of initial JSON string buffer.

BUG=v8:3925
LOG=NO

Review URL: https://codereview.chromium.org/1123013002

Cr-Commit-Position: refs/heads/master@{#28225}

src/json-parser.h

@@ -180,7 +180,7 @@ class JsonParser BASE_EMBEDDED {
   inline Factory* factory() { return factory_; }
   inline Handle<JSFunction> object_constructor() { return object_constructor_; }
 
-  static const int kInitialSpecialStringLength = 1024;
+  static const int kInitialSpecialStringLength = 32;
   static const int kPretenureTreshold = 100 * 1024;