[turbofan] WIP Support vector IC feedback in the JSTypeFeedbackTable.

test/mjsunit/unbox-double-field-indexed.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.
+
+// Flags: --allow-natives-syntax
+
+function Foo(x) {
+  this.x = x;
+}
+
+var f = new Foo(1.25);
+var g = new Foo(2.25);
+
+function add(a, b) {
+  var name = "x";
+  return a[name] + b[name];
+}
+
+assertEquals(3.5, add(f, g));
+assertEquals(3.5, add(g, f));
+%OptimizeFunctionOnNextCall(add);
+assertEquals(3.5, add(f, g));
+assertEquals(3.5, add(g, f));