AAPT2: Fix inclusion of comments in R.java javadoc

Comments weren't being copied when merged from the various
resource tables.

Also refactored the JavaClassGenerator to omit a class
if no entries exist for it.

Change-Id: I6eaa89b7b3715bc05403635a2baf0d1db3efd142
diff --git a/tools/aapt2/java/ManifestClassGenerator_test.cpp b/tools/aapt2/java/ManifestClassGenerator_test.cpp
index 1b5bc05..4081287 100644
--- a/tools/aapt2/java/ManifestClassGenerator_test.cpp
+++ b/tools/aapt2/java/ManifestClassGenerator_test.cpp
@@ -39,8 +39,9 @@
 
     std::string actual = out.str();
 
-    const size_t permissionClassPos = actual.find("public static class permission {");
-    const size_t permissionGroupClassPos = actual.find("public static class permission_group {");
+    const size_t permissionClassPos = actual.find("public static final class permission {");
+    const size_t permissionGroupClassPos =
+            actual.find("public static final class permission_group {");
     ASSERT_NE(std::string::npos, permissionClassPos);
     ASSERT_NE(std::string::npos, permissionGroupClassPos);
 
@@ -113,7 +114,7 @@
      * @hide
      * @SystemApi
      */
-    @android.annotations.SystemApi
+    @android.annotation.SystemApi
     public static final String SECRET="android.permission.SECRET";)EOF"));
 }