DM: dump a zero-results .json file right at startup.

dm/DM.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "CrashHandler.h"
 #include "DMJsonWriter.h"
 #include "DMSrcSink.h"
@@ skipping 1062 matching lines @@
     return nullptr;
 }
 
 #undef PORTABLE_FONT_PREFIX
 
 extern SkTypeface* (*gCreateTypefaceDelegate)(const char [], SkTypeface::Style );
 
 int dm_main();
 int dm_main() {
     SetupCrashHandler();
+    JsonWriter::DumpJson();  // It's handy for the bots to assume this is ~never missing.
     SkAutoGraphics ag;
     SkTaskGroup::Enabler enabled(FLAGS_threads);
     gCreateTypefaceDelegate = &create_from_name;
 
     start_keepalive();
 
     gather_gold();
     gather_uninteresting_hashes();
 
     gather_srcs();
@@ skipping 151 matching lines @@
                                                            Reporter* reporter,
                                                            GrContextFactory* factory);
 } // namespace skiatest
 
 #if !defined(SK_BUILD_FOR_IOS)
 int main(int argc, char** argv) {
     SkCommandLineFlags::Parse(argc, argv);
     return dm_main();
 }
 #endif