Start isolates in a separate thread.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 2ff605fe1a9ca736bb0997f20626a039a28286e0..6d201578f04cc8f730de93eb0c714d9937e34e97 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -2407,6 +2407,8 @@ static const char* NewConstChar(const char* chars) {
 
 
 IsolateSpawnState::IsolateSpawnState(Dart_Port parent_port,
+                                     Dart_Port origin_id,
+                                     void* init_data,
                                      const Function& func,
                                      const Instance& message,
                                      bool paused,
@@ -2415,6 +2417,8 @@ IsolateSpawnState::IsolateSpawnState(Dart_Port parent_port,
                                      Dart_Port on_error_port)
     : isolate_(NULL),
       parent_port_(parent_port),
+      origin_id_(origin_id),
+      init_data_(init_data),
       on_exit_port_(on_exit_port),
       on_error_port_(on_error_port),
       script_url_(NULL),
@@ -2452,6 +2456,7 @@ IsolateSpawnState::IsolateSpawnState(Dart_Port parent_port,
 
 
 IsolateSpawnState::IsolateSpawnState(Dart_Port parent_port,
+                                     void* init_data,
                                      const char* script_url,
                                      const char* package_root,
                                      const char** package_map,
@@ -2463,6 +2468,8 @@ IsolateSpawnState::IsolateSpawnState(Dart_Port parent_port,
                                      Dart_Port on_error_port)
     : isolate_(NULL),
       parent_port_(parent_port),
+      origin_id_(ILLEGAL_PORT),
+      init_data_(init_data),
       on_exit_port_(on_exit_port),
       on_error_port_(on_error_port),
       script_url_(script_url),