Android: Reapply changes to Google licensing lib from #24145

But document them better this time.

platform/android/java/THIRDPARTY.md

@@ -3,41 +3,16 @@
 This file list third-party libraries used in the Android source folder,
 with their provenance and, when relevant, modifications made to those files.
 
-## Google's vending library
+## Google's licensing library
 
-- Upstream: https://github.com/google/play-licensing/tree/master/lvl_library/src/main/java/com/google/android/vending
+- Upstream: https://github.com/google/play-licensing/tree/master/lvl_library/
 - Version: git (eb57657, 2018) with modifications
 - License: Apache 2.0
 
-Overwrite all files under `com/google/android/vending`.
+Overwrite all files under:
 
-Modify those files to avoid compile error and lint warning:
+- `aidl/com/android/vending/licensing`
+- `src/com/google/android/vending/licensing`
 
-- `com/google/android/vending/licensing/util/Base64.java`
-
-```diff
-@@ -338,7 +338,8 @@ public class Base64 {
-                        e += 4;
-                }
- 
--               assert (e == outBuff.length);
-+               if (BuildConfig.DEBUG && e != outBuff.length)
-+                       throw new RuntimeException();
-                return outBuff;
-        }
-```
-
-- `com/google/android/vending/licensing/LicenseChecker.java`
-
-```diff
-@@ -29,8 +29,8 @@ import android.os.RemoteException;
- import android.provider.Settings.Secure;
- import android.util.Log;
- 
--import com.android.vending.licensing.ILicenseResultListener;
--import com.android.vending.licensing.ILicensingService;
-+import com.google.android.vending.licensing.ILicenseResultListener;
-+import com.google.android.vending.licensing.ILicensingService;
- import com.google.android.vending.licensing.util.Base64;
- import com.google.android.vending.licensing.util.Base64DecoderException;
-```
+Some files have been modified to silence linter errors or fix downstream issues.
+See the `patches/com.google.android.vending.licensing.patch` file.