CefSharp v62修改方法(支持.net4.0)

吐槽一下，博客园久了没有上，账号没了，重新申请一个.

cesharp v62版本，内核采用最新的Cef 62，支持最新的Grid布局. 由于官方的cefsharp 采用.net4.5.2开发.怎么办怎么办.我只能用.net4.0.没办法啊，自己拿源码修改兼容呗.

仔细分析源码发现：

1.net4.5.2 引入了 async/await 关键字. 这个其实国外大神已经有源码放出来了，我们把代码直接引入cefsharp 这个工程. 就可以直接在4.0里使用 async/await;

2.net4.5 对task api 做了扩展， 我们只需要在.net4.0实现一下对应的api.就可以了.

3. 源码里面用了很多4.5才有的GetTypeInfo 扩展方法错误. 它返回的类型是typeinfo，不用管它，把GetTypeInfo 删掉. 直接Type 调用就可以了.

4. 对Task静态方法的扩展，需要修改一下，静态方法的调用方式.

以上是要点.下面贴源码：

本段源码是对：async/await的支持：

namespace System.Threading.Tasks
{
 public static class TaskEx
 {
 public static TaskAwaiter GetAwaiter(this Task task)
 {
  return new TaskAwaiter(task);
 }
 public static TaskAwaiter GetAwaiter(this Task task)
 {
  return new TaskAwaiter(task);
 }
 }
 public struct TaskAwaiter : INotifyCompletion
 {
 readonly Task task;
 internal TaskAwaiter(Task task)
 {
  this.task = task;
 }
 internal static TaskScheduler TaskScheduler
 {
  get
  {
  if (SynchronizationContext.Current == null)
   return TaskScheduler.Default;
  else
   return TaskScheduler.FromCurrentSynchronizationContext();
  }
 }
 public bool IsCompleted
 {
  get { return task.IsCompleted; }
 }
 public void OnCompleted(Action continuation)
 {
  this.task.ContinueWith(
  delegate (Task task) {
   continuation();
  }, TaskAwaiter.TaskScheduler);
 }
 public void GetResult()
 {
  try
  {
  task.Wait();
  }
  catch (AggregateException ex)
  {
  throw ex.InnerExceptions[0];
  }
 }
 }
 public struct TaskAwaiter : INotifyCompletion
 {
 readonly Task task;
 internal TaskAwaiter(Task task)
 {
  this.task = task;
 }
 public bool IsCompleted
 {
  get { return task.IsCompleted; }
 }
 public void OnCompleted(Action continuation)
 {
  this.task.ContinueWith(
  delegate (Task task) {
   continuation();
  }, TaskAwaiter.TaskScheduler);
 }
 public T GetResult()
 {
  try
  {
  return task.Result;
  }
  catch (AggregateException ex)
  {
  throw ex.InnerExceptions[0];
  }
 }
 }
}
namespace System.Runtime.CompilerServices
{
 public interface INotifyCompletion
 {
 void OnCompleted(Action continuation);
 }
 public interface ICriticalNotifyCompletion : INotifyCompletion
 {
 [SecurityCritical]
 void UnsafeOnCompleted(Action continuation);
 }
 public interface IAsyncStateMachine
 {
 void MoveNext();
 void SetStateMachine(IAsyncStateMachine stateMachine);
 }
 public struct AsyncVoidMethodBuilder
 {
 public static AsyncVoidMethodBuilder Create()
 {
  return new AsyncVoidMethodBuilder();
 }
 public void SetException(Exception exception)
 {
  throw exception;
 }
 public void SetResult()
 {
 }
 public void SetStateMachine(IAsyncStateMachine stateMachine)
 {
  // Should not get called as we don't implement the optimization that this method is used for.
  throw new NotImplementedException();
 }
 public void Start(ref TStateMachine stateMachine) where TStateMachine : IAsyncStateMachine
 {
  stateMachine.MoveNext();
 }
 public void AwaitOnCompleted(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : INotifyCompletion where TStateMachine : IAsyncStateMachine
 {
  awaiter.OnCompleted(stateMachine.MoveNext);
 }
 public void AwaitUnsafeOnCompleted(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : ICriticalNotifyCompletion where TStateMachine : IAsyncStateMachine
 {
  awaiter.OnCompleted(stateMachine.MoveNext);
 }
 }
 public struct AsyncTaskMethodBuilder
 {
 TaskCompletionSource