[heap] Turn on v8_enable_csa_write_barrier

With this commit, write barrier is switched to use CodeStubAssembler.

Bug: chromium:749486
Change-Id: I7e0914bee971e4f3a3257740ae7c83b31f791bd9
Reviewed-on: https://chromium-review.googlesource.com/598088Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Albert Mingkun Yang <albertnetymk@google.com>
Cr-Commit-Position: refs/heads/master@{#48006}

BUILD.gn

@@ -84,7 +84,7 @@ declare_args() {
   v8_enable_concurrent_marking = false
 
   # Sets -dV8_CSA_WRITE_BARRIER
-  v8_enable_csa_write_barrier = false
+  v8_enable_csa_write_barrier = true
 
   # Build the snapshot with unwinding information for perf.
   # Sets -dV8_USE_SNAPSHOT_WITH_UNWINDING_INFO.