anchor.diff:    }
   
     Future ensurePlatformUris() async {
  -    if (platformBinaries == null) {
  -      platformBinaries = computePlatformBinariesLocation();
  +    if (platformUri == null) {
         platformUri = platformBinaries.resolve("vm_platform.dill");
         outlineUri = platformBinaries
             .resolve(strongMode ? "vm_outline_strong.dill" : "vm_outline.dill");
  
positive.code:   FastaContext(
        this.vm,
        this.strongMode,
        this.onlyCrashes,
        bool ignoreExpectations,
        bool updateExpectations,
  
negative.code:     bool updateExpectations = environment["updateExpectations"] == "true";
      bool updateComments = environment["updateComments"] == "true";
      bool skipVm = environment["skipVm"] == "true";
      String platformBinaries = environment["platformBinaries"];
      if (platformBinaries != null && !platformBinaries.endsWith('/')) {
        platformBinaries = '$platformBinaries/';
      }
      String astKindString = environment[AST_KIND_INDEX];
      AstKind astKind =
          astKindString == null ? null : AstKind.values[int.parse(astKindString)];
      return new FastaContext(
          vm,
          strongMode,
          platformBinaries == null
              ? computePlatformBinariesLocation()
              : Uri.base.resolve(platformBinaries),
          onlyCrashes,
          ignoreExpectations,
          updateExpectations,
  