Use debug artifacts on mac host and update engine revision. (#3875)

bin/cache/engine.version

-befe39324ed5502807608496fd822fa889c5b931
+57edc534d69031b03409e7af37cbc492cb135086

packages/flutter_tools/lib/src/build_configuration.dart

@@ -37,7 +37,7 @@ enum HostPlatform {
 String getNameForHostPlatform(HostPlatform platform) {
   switch (platform) {
     case HostPlatform.darwin_x64:
-      return "mac_release";
+      return "mac_debug";
     case HostPlatform.linux_x64:
       return "linux-x64";
   }
@@ -64,7 +64,7 @@ String getNameForTargetPlatform(TargetPlatform platform) {
     case TargetPlatform.ios:
       return "ios_release";
     case TargetPlatform.darwin_x64:
-      return "mac_release";
+      return "mac_debug";
     case TargetPlatform.linux_x64:
       return "linux-x64";
   }

packages/flutter_tools/lib/src/cache.dart

@@ -207,7 +207,7 @@ class FlutterEngine {
   // Return a list of (cache directory path, download URL path) tuples.
   List<List<String>> _getToolsDirs() {
     if (Platform.isMacOS)
-      return <List<String>>[<String>['mac_release', 'mac_release/artifacts.zip']];
+      return <List<String>>[<String>['mac_debug', 'mac_debug/artifacts.zip']];
     else if (Platform.isLinux)
       return <List<String>>[
         <String>['linux-x64', 'linux-x64/artifacts.zip'],