[heap] Increase scope of CodeSpaceMemoryModificationScope to incorporate all code space writes.

Bug: chromium:774108,v8:6792
Change-Id: I7a458991921b5241c11db8999be433f4b33ce639
Reviewed-on: https://chromium-review.googlesource.com/738144Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48970}

src/heap/heap.cc

@@ -1651,6 +1651,8 @@ void Heap::MarkCompact() {
 
   uint64_t size_of_objects_before_gc = SizeOfObjects();
 
+  CodeSpaceMemoryModificationScope code_modifcation(this);
+
   mark_compact_collector()->Prepare();
 
   ms_count_++;

src/heap/mark-compact.cc

@@ -3754,7 +3754,6 @@ void MarkCompactCollector::Sweeper::AddSweptPageSafe(PagedSpace* space,
 void MarkCompactCollector::Evacuate() {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE);
   base::LockGuard<base::Mutex> guard(heap()->relocation_mutex());
-  CodeSpaceMemoryModificationScope code_modifcation(heap());
 
   {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_EVACUATE_PROLOGUE);