Issue #2184 - Increase mozjemalloc page cache size from 1 MiB to 16 MiB.

We don't need the reduced memory overhead as we are not using e10s. This
should speed up JS by a point according to Speedometer 2.1.

memory/mozjemalloc/jemalloc.c

@@ -401,7 +401,7 @@ void *_mmap(void *addr, size_t length, int prot, int flags,
  */
 #define	CHUNK_2POW_DEFAULT	20
 /* Maximum number of dirty pages per arena. */
-#define	DIRTY_MAX_DEFAULT	(1U << 8)
+#define	DIRTY_MAX_DEFAULT	(1U << 12)
 
 /*
  * Maximum size of L1 cache line.  This is used to avoid cache line aliasing,