Rework error handling in the service protocol and in Observatory.

runtime/vm/profiler_service.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/profiler_service.h"
 
 #include "vm/growable_array.h"
 #include "vm/native_symbol.h"
 #include "vm/object.h"
 #include "vm/os.h"
@@ skipping 2148 matching lines @@
 };
 
 
 void ProfilerService::PrintJSON(JSONStream* stream, TagOrder tag_order) {
   Isolate* isolate = Isolate::Current();
   // Disable profile interrupts while processing the buffer.
   Profiler::EndExecution(isolate);
   MutexLocker profiler_data_lock(isolate->profiler_data_mutex());
   IsolateProfilerData* profiler_data = isolate->profiler_data();
   if (profiler_data == NULL) {
-    JSONObject error(stream);
-    error.AddProperty("type", "Error");
-    error.AddProperty("text", "Isolate does not have profiling enabled.");
+    stream->PrintError(kProfilingDisabled, NULL);
     return;
   }
   SampleBuffer* sample_buffer = profiler_data->sample_buffer();
   ASSERT(sample_buffer != NULL);
   ScopeTimer sw("ProfilerService::PrintJSON", FLAG_trace_profiler);
   {
     StackZone zone(isolate);
     HANDLESCOPE(isolate);
     {
       // Live code holds Dart, Native, and Collected CodeRegions.
@@ skipping 182 matching lines @@
   ASSERT(sample_buffer != NULL);
 
   ClearProfileVisitor clear_profile(isolate);
   sample_buffer->VisitSamples(&clear_profile);
 
   // Enable profile interrupts.
   Profiler::BeginExecution(isolate);
 }
 
 }  // namespace dart