[vm] Cleanup some workaround due to native extensions (which got removed)

Now that support for native extensions (aka dart-ext:*) has been
removed, the kernel loader is guaranteed not to call out to embedder
anymore (it did so before for loading shared libraries).

This allos us to clean up some code as well as extend the scope of our
NoActiveIsolateScope.

TEST=ci

Change-Id: I5c8c9ee47298fdd316583ba3aed74772c1c7783f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/212296
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

runtime/observatory/tests/service/get_vm_timeline_rpc_test.dart

@@ -112,8 +112,11 @@ void allEventsHaveIsolateNumber(List events) {
     expect(arguments, isA<Map>());
     expect(arguments['isolateGroupId'], isA<String>());
     if (!const ['GC', 'Compiler', 'CompilerVerbose'].contains(event['cat']) &&
-        !const ['FinishTopLevelClassLoading', 'FinishClassLoading']
-            .contains(event['name'])) {
+        !const [
+          'FinishTopLevelClassLoading',
+          'FinishClassLoading',
+          'ProcessPendingClasses'
+        ].contains(event['name'])) {
       expect(arguments['isolateId'], isA<String>());
     }
   }

runtime/observatory_2/tests/service_2/get_vm_timeline_rpc_test.dart

@@ -112,8 +112,11 @@ void allEventsHaveIsolateNumber(List events) {
     expect(arguments, isA<Map>());
     expect(arguments['isolateGroupId'], isA<String>());
     if (!const ['GC', 'Compiler', 'CompilerVerbose'].contains(event['cat']) &&
-        !const ['FinishTopLevelClassLoading', 'FinishClassLoading']
-            .contains(event['name'])) {
+        !const [
+          'FinishTopLevelClassLoading',
+          'FinishClassLoading',
+          'ProcessPendingClasses'
+        ].contains(event['name'])) {
       expect(arguments['isolateId'], isA<String>());
     }
   }

runtime/vm/isolate.h

@@ -1774,31 +1774,10 @@ class NoActiveIsolateScope : public StackResource {
   }
 
  private:
-  friend class DisabledNoActiveIsolateScope;
   Thread* thread_;
   Isolate* saved_isolate_;
 };
 
-// Can be used inside a [NoActiveIsolateScope] to set the current isolate.
-class DisabledNoActiveIsolateScope : public StackResource {
- public:
-  explicit DisabledNoActiveIsolateScope(NoActiveIsolateScope* scope)
-      : StackResource(Thread::Current()),
-        thread_(static_cast<Thread*>(thread())),
-        scope_(scope) {
-    ASSERT(thread_->isolate() == nullptr);
-    thread_->isolate_ = scope_->saved_isolate_;
-  }
-  ~DisabledNoActiveIsolateScope() {
-    ASSERT(thread_->isolate_ == scope_->saved_isolate_);
-    thread_->isolate_ = nullptr;
-  }
-
- private:
-  Thread* thread_;
-  NoActiveIsolateScope* scope_;
-};
-
 }  // namespace dart
 
 #endif  // RUNTIME_VM_ISOLATE_H_

runtime/vm/kernel_loader.cc

@@ -189,7 +189,7 @@ KernelLoader::KernelLoader(Program* program,
     : program_(program),
       thread_(Thread::Current()),
       zone_(thread_->zone()),
-      isolate_(thread_->isolate()),
+      no_active_isolate_scope_(),
       patch_classes_(Array::ZoneHandle(zone_)),
       active_class_(),
       library_kernel_offset_(-1),  // Set to the correct value in LoadLibrary
@@ -462,7 +462,7 @@ KernelLoader::KernelLoader(const Script& script,
     : program_(NULL),
       thread_(Thread::Current()),
       zone_(thread_->zone()),
-      isolate_(thread_->isolate()),
+      no_active_isolate_scope_(),
       patch_classes_(Array::ZoneHandle(zone_)),
       library_kernel_offset_(data_program_offset),
       kernel_binary_version_(kernel_binary_version),
@@ -646,8 +646,6 @@ ObjectPtr KernelLoader::LoadProgram(bool process_pending_classes) {
 }
 
 void KernelLoader::LoadLibrary(const Library& library) {
-  NoActiveIsolateScope no_active_isolate_scope;
-
   // This will be invoked by VM bootstrapping code.
   SafepointWriteRwLocker ml(thread_, thread_->isolate_group()->program_lock());
 
@@ -874,8 +872,6 @@ LibraryPtr KernelLoader::LoadLibrary(intptr_t index) {
         "not allowed");
   }
 
-  NoActiveIsolateScope no_active_isolate_scope;
-
   // Read library index.
   library_kernel_offset_ = library_offset(index);
   correction_offset_ = library_kernel_offset_;
@@ -1690,8 +1686,6 @@ void KernelLoader::FinishClassLoading(const Class& klass,
 }
 
 void KernelLoader::FinishLoading(const Class& klass) {
-  NoActiveIsolateScope no_active_isolate_scope;
-
   ASSERT(klass.IsTopLevel() || (klass.kernel_offset() > 0));
 
   Zone* zone = Thread::Current()->zone();

runtime/vm/kernel_loader.h

@@ -375,7 +375,7 @@ class KernelLoader : public ValueObject {
 
   Thread* thread_;
   Zone* zone_;
-  Isolate* isolate_;
+  NoActiveIsolateScope no_active_isolate_scope_;
   Array& patch_classes_;
   ActiveClass active_class_;
   // This is the offset of the current library within

runtime/vm/object.cc

@@ -13639,11 +13639,13 @@ static ObjectPtr EvaluateCompiledExpressionHelper(
         zone, String::New("Kernel isolate returned ill-formed kernel.")));
   }
 
-  kernel::KernelLoader loader(kernel_pgm.get(),
-                              /*uri_to_source_table=*/nullptr);
-  auto& result = Object::Handle(
-      zone, loader.LoadExpressionEvaluationFunction(library_url, klass));
-  kernel_pgm.reset();
+  auto& result = Object::Handle(zone);
+  {
+    kernel::KernelLoader loader(kernel_pgm.get(),
+                                /*uri_to_source_table=*/nullptr);
+    result = loader.LoadExpressionEvaluationFunction(library_url, klass);
+    kernel_pgm.reset();
+  }
 
   if (result.IsError()) return result.ptr();