WIP: DevFS initial implementation

runtime/vm/json_stream.cc

Index: runtime/vm/json_stream.cc
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 003f1b36d3c76a91340a6ab3dbfadf43be15d4af..ca01e60b7dc4839a005478d7f7073cbf7daab0b8 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -83,6 +83,7 @@ void JSONStream::Setup(Zone* zone,
     const char** param_values_native =
         zone->Alloc<const char*>(param_keys.Length());
     for (intptr_t i = 0; i < param_keys.Length(); i++) {
+      // fprintf(stderr, "Param %" Pd " is %s\n", i, param_values[
       string_iterator ^= param_keys.At(i);
       param_keys_native[i] =
           zone->MakeCopyOfString(string_iterator.ToCString());
@@ -130,6 +131,14 @@ static const char* GetJSONRpcErrorMessage(intptr_t code) {
       return "Isolate must be runnable";
     case kIsolateMustBePaused:
       return "Isolate must be paused";
+    case kIsolateIsReloading:
+      return "Isolate is reloading";
+    case kFileSystemAlreadyExists:
+      return "File system already exists";
+    case kFileSystemDoesNotExist:
+      return "File system does not exist";
+    case kFileDoesNotExist:
+      return "File does not exist";
     default:
       return "Extension error";
   }