Add an API for setting the sticky error

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 aff9955d0f6066674e0b6dc52f2389bf321cc290..567fc848b588b6ebfb54a80fe204b0f24c431ac3 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1450,6 +1450,31 @@ DART_EXPORT void Dart_SetPausedOnExit(bool paused) {
 }
 
 
+DART_EXPORT void Dart_SetStickyError(Dart_Handle error) {
+  Thread* thread = Thread::Current();
+  Isolate* isolate = thread->isolate();
+  CHECK_ISOLATE(isolate);

[siva, 2016/08/08 17:53:45]

Probably better to create a scope here as we will be creating a handle below
when Api::UnwrapErrorHandle is called. If this function is called too many times
we might end up with handles in the top most scope (kind of a leak).

DARTSCOPE(Thread::Current());
Isolate* I = T->isolate();

[Cutch, 2016/08/08 19:14:30]

Done.

+  NoSafepointScope no_safepoint_scope;
+  if (isolate->sticky_error() != Error::null()) {
+    FATAL1("%s expects there to be no sticky error.", CURRENT_FUNC);
+  }
+  if (!Dart_IsUnhandledExceptionError(error)) {
+    FATAL1("%s expects the error to be an unhandled exception error.",
+            CURRENT_FUNC);
+  }
+  isolate->SetStickyError(
+      Api::UnwrapErrorHandle(thread->zone(), error).raw());

[siva, 2016/08/08 17:53:45]

you could use Z here instead of thread->zone() to be consistent with the rest of
the file.

[Cutch, 2016/08/08 19:14:30]

Done.

+}
+
+
+DART_EXPORT bool Dart_HasStickyError() {
+  Isolate* isolate = Isolate::Current();
+  CHECK_ISOLATE(isolate);
+  NoSafepointScope no_safepoint_scope;
+  return isolate->sticky_error() != Error::null();
+}
+
+
 DART_EXPORT void Dart_ExitIsolate() {
   Thread* T = Thread::Current();
   CHECK_ISOLATE(T->isolate());