Fix uncommon GC related reload crash

runtime/vm/isolate_reload.cc

Index: runtime/vm/isolate_reload.cc
diff --git a/runtime/vm/isolate_reload.cc b/runtime/vm/isolate_reload.cc
index 7a867d2d8e0b00ebf29c0429e6d56f49d846df0e..71d8387b44f9bea59598051f833a7a461daf5dc0 100644
--- a/runtime/vm/isolate_reload.cc
+++ b/runtime/vm/isolate_reload.cc
@@ -190,17 +190,9 @@ IsolateReloadContext::IsolateReloadContext(Isolate* isolate, bool test_mode)
       become_map_storage_(Array::null()),
       saved_root_library_(Library::null()),
       saved_libraries_(GrowableObjectArray::null()) {
-  // Preallocate storage for maps.
-  old_classes_set_storage_ =
-      HashTables::New<UnorderedHashSet<ClassMapTraits> >(4);
-  class_map_storage_ =
-      HashTables::New<UnorderedHashMap<ClassMapTraits> >(4);
-  old_libraries_set_storage_ =
-      HashTables::New<UnorderedHashSet<LibraryMapTraits> >(4);
-  library_map_storage_ =
-      HashTables::New<UnorderedHashMap<LibraryMapTraits> >(4);
-  become_map_storage_ =
-      HashTables::New<UnorderedHashMap<BecomeMapTraits> >(4);
+  // NOTE: DO NOT ALLOCATE ANY RAW OBJECTS HERE. The IsolateReloadContext is not
+  // associated with the isolate yet and if a GC is triggered here the raw
+  // objects will not be properly accounted for.
 }
 
 
@@ -234,12 +226,25 @@ void IsolateReloadContext::ReportSuccess() {
 void IsolateReloadContext::StartReload() {
   TIMELINE_SCOPE(Reload);
   Thread* thread = Thread::Current();
+  ASSERT(isolate() == thread->isolate());
 
   // Grab root library before calling CheckpointBeforeReload.
   const Library& root_lib = Library::Handle(object_store()->root_library());
   ASSERT(!root_lib.IsNull());
   const String& root_lib_url = String::Handle(root_lib.url());
 
+  // Preallocate storage for maps.
+  old_classes_set_storage_ =
+      HashTables::New<UnorderedHashSet<ClassMapTraits> >(4);
+  class_map_storage_ =
+      HashTables::New<UnorderedHashMap<ClassMapTraits> >(4);
+  old_libraries_set_storage_ =
+      HashTables::New<UnorderedHashSet<LibraryMapTraits> >(4);
+  library_map_storage_ =
+      HashTables::New<UnorderedHashMap<LibraryMapTraits> >(4);
+  become_map_storage_ =
+      HashTables::New<UnorderedHashMap<BecomeMapTraits> >(4);
+
   // Disable the background compiler while we are performing the reload.
   BackgroundCompiler::Disable();