Tune heuristics a bit.

First version. Seems to be more in line with what we're seeing.

Change-Id: I5117352c13cb2e95d16f0c9b05b1faf37c05d710
diff --git a/runtime/jit/jit_code_cache.cc b/runtime/jit/jit_code_cache.cc
index 2596dd9..60568b2 100644
--- a/runtime/jit/jit_code_cache.cc
+++ b/runtime/jit/jit_code_cache.cc
@@ -57,9 +57,9 @@
     return nullptr;
   }
 
-  // Data cache is 1 / 4 of the map.
+  // Data cache is 1 / 2 of the map.
   // TODO: Make this variable?
-  size_t data_size = RoundUp(data_map->Size() / 4, kPageSize);
+  size_t data_size = RoundUp(data_map->Size() / 2, kPageSize);
   size_t code_size = data_map->Size() - data_size;
   uint8_t* divider = data_map->Begin() + data_size;