Rework error handling in the service protocol and in Observatory.

runtime/observatory/lib/src/elements/script_inset.dart

Index: runtime/observatory/lib/src/elements/script_inset.dart
diff --git a/runtime/observatory/lib/src/elements/script_inset.dart b/runtime/observatory/lib/src/elements/script_inset.dart
index 164c134a0b654b689b710d3a2a2736148faec24e..17c110db290cd24f8f3a2a4301798d267287bf42 100644
--- a/runtime/observatory/lib/src/elements/script_inset.dart
+++ b/runtime/observatory/lib/src/elements/script_inset.dart
@@ -459,7 +459,10 @@ class ScriptInsetElement extends ObservatoryElement {
       e.classes.clear();
       e.classes.add('noCopy');
 
-      if (busy) {
+      if (!line.possibleBpt) {
+        e.classes.add("emptyBreakpoint");
+        e.text = nbsp;
+      } else if (busy) {
         e.classes.add("busyBreakpoint");
       } else {
         if (line.breakpoints != null) {
@@ -484,6 +487,15 @@ class ScriptInsetElement extends ObservatoryElement {
         line.script.isolate.addBreakpoint(line.script, line.line).then((_) {
           busy = false;
           update();
+        }).catchError((e, st) {
+          bool suppressError = false;
+          if (e is ServerRpcException) {
+            ServerRpcException se = e;
+            suppressError = (se.code == ServerRpcException.kNoBreakAtLine);
+          }
+          if (!suppressError) {
+            return new Future.error(e, st);

[Cutch, 2015/05/13 17:50:09]

Maybe cleaner as:

if (e is ServiceRpcException && se.code == ...) {
  return new Future.value(null);
}

return new Future.error(e, st);

[turnidge, 2015/05/14 17:53:43]

Rewritten.

+          }
         });
       } else {
         // Existing breakpoint.  Remove it.