Enables clean VM shutdown.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 6536e08d26540ffeb475b6a4e8127a3b38d596e7..71ce42ea446a9fde9e14803f43909c8a982d6396 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1263,7 +1263,7 @@ DART_EXPORT const char* Dart_VersionString() {
   return Version::String();
 }
 
-DART_EXPORT bool Dart_Initialize(
+DART_EXPORT char* Dart_Initialize(
     const uint8_t* vm_isolate_snapshot,
     Dart_IsolateCreateCallback create,
     Dart_IsolateInterruptCallback interrupt,
@@ -1279,21 +1279,19 @@ DART_EXPORT bool Dart_Initialize(
                                        file_open, file_read, file_write,
                                        file_close, entropy_source);
   if (err_msg != NULL) {
-    OS::PrintErr("Dart_Initialize: %s\n", err_msg);

[turnidge, 2015/08/04 21:39:02]

So the embedders that haven't been updated to deal with the new return value
will not print the error for a while, until they are updated.  Can you update
the Mojo embedder in a follow-up CL to handle this?

[zra, 2015/08/05 06:23:06]

Acknowledged.

-    return false;
+    return strdup(err_msg);
   }
-  return true;
+  return NULL;
 }
 
 
-DART_EXPORT bool Dart_Cleanup() {
+DART_EXPORT char* Dart_Cleanup() {
   CHECK_NO_ISOLATE(Isolate::Current());
   const char* err_msg = Dart::Cleanup();
   if (err_msg != NULL) {
-    OS::PrintErr("Dart_Cleanup: %s\n", err_msg);
-    return false;
+    return strdup(err_msg);
   }
-  return true;
+  return NULL;
 }
 
 
@@ -1364,6 +1362,10 @@ DART_EXPORT Dart_Isolate Dart_CreateIsolate(const char* script_uri,
   }
   Isolate* isolate = Dart::CreateIsolate(isolate_name, *flags);
   free(isolate_name);
+  if (isolate == NULL) {
+    *error = strdup("Isolate creation failed");
+    return reinterpret_cast<Dart_Isolate>(NULL);
+  }
   StackZone zone(isolate);
   HANDLESCOPE(isolate);
   // We enter an API scope here as InitializeIsolate could compile some