Enable error prone against all CTS harness subproject

Also fix the issue reported with error build current rules.

Test: make cts javac-check -j64 RUN_ERROR_PRONE=true
Bug: 37854485
Change-Id: If5e9ffd6fbf5caf14e9ef88f2e745c000c6a2df8
diff --git a/error_prone_rules.mk b/error_prone_rules.mk
index 96b340e..c2b0c79 100644
--- a/error_prone_rules.mk
+++ b/error_prone_rules.mk
@@ -17,6 +17,7 @@
                           -Xep:BoxedPrimitiveConstructor:ERROR \
                           -Xep:ConstantField:ERROR \
                           -Xep:FormatString:ERROR \
+                          -Xep:GetClassOnClass:ERROR \
                           -Xep:JUnitAmbiguousTestClass:ERROR \
                           -Xep:MissingFail:ERROR \
                           -Xep:MissingOverride:ERROR \