[vm/isolates] Clean up redundant SafepointOperationScope when installing allocation stub.

The SafepointOperationScope is provided by RunWithStoppedMutators.

Change-Id: Ib0f3a86de58b074a0b5b84b05631ecc59d62de36
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153640
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

Author: aam

runtime/vm/compiler/jit/compiler.cc

@@ -659,7 +659,7 @@ CodePtr CompileParsedFunctionHelper::Compile(CompilationPipeline* pipeline) {
         //      those writes are observed atomically.
         //
         thread()->isolate_group()->RunWithStoppedMutators(
-            install_code_fun, install_code_fun, /*use_force_growth=*/true);
+            install_code_fun, /*use_force_growth=*/true);
       }
       if (!result->IsNull()) {
         // Must be called outside of safepoint.

runtime/vm/stub_code.cc

@@ -220,7 +220,7 @@ CodePtr StubCode::GetAllocationStubForClass(const Class& cls) {
       }
     };
     auto bg_compiler_fun = [&]() {
-      ForceGrowthSafepointOperationScope safepoint_scope(thread);
+      ASSERT(Thread::Current()->IsAtSafepoint());
       stub = cls.allocation_stub();
       // Check if stub was already generated.
       if (!stub.IsNull()) {

runtime/vm/type_testing_stubs.cc

@@ -226,8 +226,8 @@ CodePtr TypeTestingStubGenerator::BuildCodeForType(const Type& type) {
   //   a) We allocate an instructions object, which might cause us to
   //      temporarily flip page protections from (RX -> RW -> RX).
   //
-  thread->isolate_group()->RunWithStoppedMutators(
-      install_code_fun, install_code_fun, /*use_force_growth=*/true);
+  thread->isolate_group()->RunWithStoppedMutators(install_code_fun,
+                                                  /*use_force_growth=*/true);
 
   Code::NotifyCodeObservers(name, code, /*optimized=*/false);