Implement 'print', 'up', 'down', and 'frame' commands in the Observatory debugger.

runtime/vm/service.cc

Index: runtime/vm/service.cc
diff --git a/runtime/vm/service.cc b/runtime/vm/service.cc
index 0a638c1f972a6d2dd43d2937d5f8fb5a65e7198b..d38c74733f54018da83dd7ee360c1f47f535bc25 100644
--- a/runtime/vm/service.cc
+++ b/runtime/vm/service.cc
@@ -1519,6 +1519,32 @@ static bool Eval(Isolate* isolate, JSONStream* js) {
 }
 
 
+static const MethodParameter* eval_frame_params[] = {
+  ISOLATE_PARAMETER,
+  new UIntParameter("frame", true),
+  new MethodParameter("expression", true),
+  NULL,
+};
+
+
+static bool EvalFrame(Isolate* isolate, JSONStream* js) {
+  DebuggerStackTrace* stack = isolate->debugger()->StackTrace();
+  intptr_t framePos = UIntParameter::Parse(js->LookupParam("frame"));
+  if (framePos > stack->Length()) {
+    PrintInvalidParamError(js, "frame");
+    return true;
+  }
+  ActivationFrame* frame = stack->FrameAt(framePos);
+
+  const char* expr = js->LookupParam("expression");
+  const String& expr_str = String::Handle(isolate, String::New(expr));
+
+  const Object& result = Object::Handle(frame->Evaluate(expr_str));
+  result.PrintJSON(js, true);
+  return true;
+}
+
+
 static const MethodParameter* get_call_site_data_params[] = {
   ISOLATE_PARAMETER,
   new IdParameter("targetId", true),
@@ -2506,6 +2532,8 @@ static ServiceMethodDescriptor service_methods_[] = {
     clear_cpu_profile_params },
   { "eval", Eval,
     eval_params },
+  { "evalFrame", EvalFrame,
+    eval_frame_params },
   { "getAllocationProfile", GetAllocationProfile,
     get_allocation_profile_params },
   { "getCallSiteData", GetCallSiteData,