[heap] Make {NewOffHeapTrampolineFor} use finer scope.

This makes the above factory function use a fine-grained scope when
unlocking code space for modification. It is now based on the memory
chunk of the resulting code object.

R=ulan@chromium.org

Change-Id: Iabe6fba7595ba3264b21bcd6f6634ab9725eaad9
Reviewed-on: https://chromium-review.googlesource.com/c/1335687Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57498}

src/heap/factory.cc

@@ -2692,8 +2692,13 @@ Handle<Code> Factory::NewOffHeapTrampolineFor(Handle<Code> code,
   // The trampoline code object must inherit specific flags from the original
   // builtin (e.g. the safepoint-table offset). We set them manually here.
 
+  {
+    MemoryChunk* chunk = MemoryChunk::FromAddress(result->ptr());
+    CodePageMemoryModificationScope code_allocation(chunk);
+
     const bool set_is_off_heap_trampoline = true;
-  const int stack_slots = code->has_safepoint_info() ? code->stack_slots() : 0;
+    const int stack_slots =
+        code->has_safepoint_info() ? code->stack_slots() : 0;
     result->initialize_flags(code->kind(), code->has_unwinding_info(),
                              code->is_turbofanned(), stack_slots,
                              set_is_off_heap_trampoline);
@@ -2707,8 +2712,8 @@ Handle<Code> Factory::NewOffHeapTrampolineFor(Handle<Code> code,
     }
 
     // Replace the newly generated trampoline's RelocInfo ByteArray with the
-  // canonical one stored in the roots to avoid duplicating it for every single
-  // builtin.
+    // canonical one stored in the roots to avoid duplicating it for every
+    // single builtin.
     ByteArray* canonical_reloc_info =
         ReadOnlyRoots(isolate()).off_heap_trampoline_relocation_info();
 #ifdef DEBUG
@@ -2720,6 +2725,7 @@ Handle<Code> Factory::NewOffHeapTrampolineFor(Handle<Code> code,
     }
 #endif
     result->set_relocation_info(canonical_reloc_info);
+  }
 
   return result;
 }

src/isolate.cc

@@ -3024,7 +3024,6 @@ void CreateOffHeapTrampolines(Isolate* isolate) {
 
   EmbeddedData d = EmbeddedData::FromBlob();
 
-  CodeSpaceMemoryModificationScope code_allocation(isolate->heap());
   for (int i = 0; i < Builtins::builtin_count; i++) {
     if (!Builtins::IsIsolateIndependent(i)) continue;