Move more parts of stack trace formatting to runtime.

test/mjsunit/stack-traces-custom.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var o = { f: function() { throw new Error(); } };
+o.g = function() { o.f() }
+
+Error.prepareStackTrace = function(e, frames) { return frames; }
+
+try {
+  o.g();
+} catch (e) {
+  var frames = e.stack;
+  assertEquals("f", frames[0].getMethodName());
+  assertEquals("g", frames[1].getMethodName());
+  assertEquals(null, frames[2].getMethodName());
+}