Add a rule for equality check

- Put protos in their own target to avoid the generated
files from being included in error_prone checks.

Test: local run, unit tests
Bug: 35864476
Change-Id: Ifcb250e7c19ddc17f9df653d71620e0811930403
diff --git a/src/com/android/media/tests/CameraSettingsTest.java b/src/com/android/media/tests/CameraSettingsTest.java
index 12bb0cf..d5fe0dd 100644
--- a/src/com/android/media/tests/CameraSettingsTest.java
+++ b/src/com/android/media/tests/CameraSettingsTest.java
@@ -151,7 +151,7 @@
             reader = new BufferedReader(new FileReader(outputFile));
 
             while ((line = reader.readLine()) != null) {
-                if (line != "") {
+                if (!line.isEmpty()) {
                     lines.add(line);
                 }
             }