Add android.jar for Android master (from AOSP master build)

Content of README.google:

Name: Android system library jar
URL: https://developer.android.com/studio/index.html
Version: API version U (From AOSP build ID 8952595)
Revision: NA
License: Apache License Version 2.0

Description:
This is the android.jar pulled from build bot.

Bug: 242548283
Change-Id: I7c24aef1599e55b1f012a577ad899b474fe9aea6
diff --git a/.gitignore b/.gitignore
index 5bb74e5..ada4839 100644
--- a/.gitignore
+++ b/.gitignore
@@ -40,6 +40,8 @@
 third_party/android_jar/lib
 third_party/android_jar/lib-v[0-9][0-9]
 third_party/android_jar/lib-v[0-9][0-9].tar.gz
+third_party/android_jar/lib-master
+third_party/android_jar/lib-master.tar.gz
 third_party/android_jar/lib.tar.gz
 third_party/android_jar/libcore_latest
 third_party/android_jar/libcore_latest.tar.gz