Handle function arguments inside function calls.

test/splitting/mixed.stmt

 40 columns                              |
 >>> keeps map on one line if possible
 sendPort.send({'type': 'error', 'error': 'oops'});
 <<<
 sendPort.send(
     {'type': 'error', 'error': 'oops'});
 >>> prefers to wrap before "."
 new Future.sync(() => callback('msg')).then(
     (result) => replyTo.send()).catchError((error) {});
 <<<
@@ skipping 53 matching lines @@
     argument,
     obj
         .method(argument)
         .method(argument)
         .method(() {
       body;
     }).another().another());
 >>> unnested function inside nested expression
 function(argument, function(() {;}));
 <<<
-function(
-    argument,
-    function(() {
-      ;
-    }));
+function(argument, function(() {
+  ;
+}));
 >>> nested function inside nested expression
 function(argument, function(() {;}, argument, () {;}));
 <<<
 function(
     argument,
     function(
         () {
           ;
         },
         argument,
@@ skipping 100 matching lines @@
         veryLongIdentifier -
     veryLongIdentifier;
 >>> choose extra nesting if it leads to better solution
 longIdentifier +
     (longIdentifier ? 0 :
         1) == identifier;
 <<<
 longIdentifier +
         (longIdentifier ? 0 : 1) ==
     identifier;