[heap] Turn off form space clearing per default.

Bug: chromium:860153
Change-Id: I1ad6c81f672efe2e705d5285b80e2855af828254
Reviewed-on: https://chromium-review.googlesource.com/1125726Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54200}

src/flag-definitions.h

@@ -794,7 +794,7 @@ DEFINE_BOOL(optimize_ephemerons, true,
 DEFINE_NEG_NEG_IMPLICATION(optimize_ephemerons, parallel_ephemeron_marking)
 DEFINE_NEG_NEG_IMPLICATION(optimize_ephemerons, parallel_ephemeron_visiting)
 
-DEFINE_BOOL(clear_free_memory, true, "initialize free memory with 0")
+DEFINE_BOOL(clear_free_memory, false, "initialize free memory with 0")
 
 DEFINE_BOOL(young_generation_large_objects, false,
             "allocates large objects by default in the young generation large "