Android: Fix JavaLangClash warning

The warnings is this:
org.webrtc.ClassLoader clashes with java.lang.ClassLoader

This CL fixes that by renaming org.webrtc.ClassLoader to
org.webrtc.WebRtcClassLoader.

Bug: webrtc:6597,webrtc:8534
Change-Id: Ia392850cd2d0eb0683c03607d0cec06904de532f
Reviewed-on: https://webrtc-review.googlesource.com/23680
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20715}

sdk/android/src/java/org/webrtc/WebRtcClassLoader.java

@@ -15,9 +15,9 @@ package org.webrtc;
  * what thread it's called from. Such a ClassLoader is needed for the few cases where the JNI
  * mechanism is unable to automatically determine the appropriate ClassLoader instance.
  */
-class ClassLoader {
+class WebRtcClassLoader {
   @CalledByNative
   static Object getClassLoader() {
-    return ClassLoader.class.getClassLoader();
+    return WebRtcClassLoader.class.getClassLoader();
   }
 }