Update headings to use sentence case.

sdk/lib/js/dartium/js_dartium.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Support for interoperating with JavaScript.
  * 
  * This library provides access to JavaScript objects from Dart, allowing
  * Dart code to get and set properties, and call methods of JavaScript objects
  * and invoke JavaScript functions. The library takes care of converting
@@ skipping 25 matching lines @@
  *     import 'dart:js';
  *     
  *     main() {
  *       var object = new JsObject(context['Object']);
  *       object['greeting'] = 'Hello';
  *       object['greet'] = (name) => "${object['greeting']} $name";
  *       var message = object.callMethod('greet', ['JavaScript']);
  *       context['console'].callMethod('log', [message]);
  *     }
  *
- * ## Proxying and Automatic Conversion
+ * ## Proxying and automatic conversion
  * 
  * When setting properties on a JsObject or passing arguments to a Javascript
  * method or function, Dart objects are automatically converted or proxied to
  * JavaScript objects. When accessing JavaScript properties, or when a Dart
  * closure is invoked from JavaScript, the JavaScript objects are also
  * converted to Dart.
  *
  * Functions and closures are proxied in such a way that they are callable. A
  * Dart closure assigned to a JavaScript property is proxied by a function in
  * JavaScript. A JavaScript function accessed from Dart is proxied by a
@@ skipping 312 matching lines @@
 /**
  * Returns a method that can be called with an arbitrary number (for n less
  * than 11) of arguments without violating Dart type checks.
  */
 Function _wrapAsDebuggerVarArgsFunction(JsFunction jsFunction) =>
   ([a1=_UNDEFINED, a2=_UNDEFINED, a3=_UNDEFINED, a4=_UNDEFINED,
     a5=_UNDEFINED, a6=_UNDEFINED, a7=_UNDEFINED, a8=_UNDEFINED,
     a9=_UNDEFINED, a10=_UNDEFINED]) =>
     jsFunction._applyDebuggerOnly(_stripUndefinedArgs(
         [a1,a2,a3,a4,a5,a6,a7,a8,a9,a10]));