Do not allow a hot reload if the isolate has a sticky error

runtime/vm/service.cc

Index: runtime/vm/service.cc
diff --git a/runtime/vm/service.cc b/runtime/vm/service.cc
index d29a658cb8ef19ce4523a3a58efa5dff3b43e29d..a0df953a460b0230b6351df8e457dfc315091596 100644
--- a/runtime/vm/service.cc
+++ b/runtime/vm/service.cc
@@ -2520,6 +2520,13 @@ static bool ReloadSources(Thread* thread, JSONStream* js) {
                    "A library tag handler must be installed.");
     return true;
   }
+  if ((isolate->sticky_error() != Error::null()) ||
+      (Thread::Current()->sticky_error() != Error::null())) {
+    js->PrintError(kIsolateReloadBarred,
+                   "This isolate cannot reload sources anymore because there "
+                   "was an unhandled exception error. Restart the isolate.");

[siva, 2016/08/24 17:53:24]

Would it be worth printing the error string here so folks know what the
unhandled error was?

[Cutch, 2016/08/24 18:30:49]

The clients can grab the error over the service protocol.

+    return true;
+  }
   if (isolate->IsReloading()) {
     js->PrintError(kIsolateIsReloading,
                    "This isolate is being reloaded.");