解决agent的API类在自定义的ClassLoader里加载的问题

* 默认情况下，加载java agent的是SystemClassLoader，那么应用自己定义的ClassLoader，如果parent不是 SystemClassLoader，就加载不到java agent里的类。

比如，有一个类Foo，它有一个函数bar:

```java
public class Foo {
public void bar() {

}
}
```

有一个Java Agent想做一些类增强，会插入一些代码：

```java
public class Foo {
public void bar() {
SampleAgent.log("here");
}
}
```

* 这就要求加载Foo的ClassLoader必须要能加载到SystemClassLoader里的`SampleAgent`类。

No files or tests are named. Start by tracing how the Java agent exposes SampleAgent to classes loaded by an application-defined ClassLoader whose parent is not the SystemClassLoader, then reproduce the Foo/bar example. Done means the injected SampleAgent.log("here") call can resolve and run in that loader setup.

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