Updated enable-malloc-hooks flag to be disabled by default in debug mode.

runtime/vm/flag_list.h

Index: runtime/vm/flag_list.h
diff --git a/runtime/vm/flag_list.h b/runtime/vm/flag_list.h
index c4ac29f4ed36e35d94bf3b832da30d1c972d6f37..58311147c679aa0673c9af841066f9d9c97398ec 100644
--- a/runtime/vm/flag_list.h
+++ b/runtime/vm/flag_list.h
@@ -25,12 +25,6 @@
 #define USING_MULTICORE false
 #endif
 
-#if defined(DEBUG)
-#define USING_DEBUG true
-#else
-#define USING_DEBUG false
-#endif
-
 // List of all flags in the VM.
 // Flags can be one of three categories:
 // * P roduct flags: Can be set in any of the deployment modes, including in
@@ -74,7 +68,7 @@
     "Dump megamorphic cache statistics")                                       \
   R(dump_symbol_stats, false, bool, false, "Dump symbol table statistics")     \
   R(enable_asserts, false, bool, false, "Enable assert statements.")           \
-  R(enable_malloc_hooks, false, bool, USING_DEBUG,                             \
+  R(enable_malloc_hooks, false, bool, false,                                   \
     "Enable native memory statistic collection. Enabled by default in Debug "  \
     "mode")                                                                    \
   C(enable_mirrors, false, false, bool, true,                                  \