Transmit breakpoint id on paused event

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
===================================================================
--- runtime/vm/debugger.h	(revision 31003)
+++ runtime/vm/debugger.h	(working copy)
@@ -254,13 +254,22 @@
     kIsolateInterrupted = 6,
   };
   struct DebuggerEvent {
+    explicit DebuggerEvent(EventType event_type)
+        : type(event_type) {
+      top_frame = NULL;
+      breakpoint = NULL;
+      exception = NULL;
+      isolate_id = 0;
+    }
     EventType type;
-    union {
-      ActivationFrame* top_frame;
-      SourceBreakpoint* breakpoint;
-      const Object* exception;
-      Dart_Port isolate_id;
-    };
+    // type == kBreakpointReached.
+    ActivationFrame* top_frame;
+    // type == kBreakpointResolved, kBreakpointReached.
+    SourceBreakpoint* breakpoint;
+    // type == kExceptionThrown.
+    const Object* exception;
+    // type == kIsolate(Created|Shutdown|Interrupted).
+    Dart_Port isolate_id;

[turnidge, 2013/12/10 17:17:18]

At some point this may grow out of being a struct and may be better as a tree of
classes.  Not now, but something to consider.

[hausner, 2013/12/10 17:44:37]

I try not to be baroque. It's just a struct with a function that initializes the
fields automatically when declared.

[turnidge, 2013/12/10 18:55:24]

Yeah, agreed that being unnecessarily baroque is not good.

The counter argument (which we all know) goes like this:

- we need to maintain an explicit 'type' (instead of using C++ types)
- we need to sometimes use a field or not depending on the 'type', enforced by
convetion (instead of using subclassing, enforced by compiler)
- we probably have some dispatching code somewhere based on this 'type' (instead
of virtual dispatch)

Don't care for this review, though.

   };
   typedef void EventHandler(DebuggerEvent *event);
 
@@ -391,7 +400,8 @@
                                      const Code& code);
   static DebuggerStackTrace* CollectStackTraceNew();
   void SignalBpResolved(SourceBreakpoint *bpt);
-  void SignalPausedEvent(ActivationFrame* top_frame);
+  void SignalPausedEvent(ActivationFrame* top_frame,
+                         SourceBreakpoint* breakpoint);
 
   intptr_t nextId() { return next_id_++; }