Add signature|system permission to MediaDrm signer APIs

Also addresses style issues noted in post-submit review from
https://googleplex-android-review.git.corp.google.com/#/c/439054/

Change-Id: If177b11dbcc049bc271529c119bc5c36ae0107b5
related-to-bug: 12702350
diff --git a/media/jni/android_media_MediaDrm.cpp b/media/jni/android_media_MediaDrm.cpp
index 1dbaa3a..7c45682 100644
--- a/media/jni/android_media_MediaDrm.cpp
+++ b/media/jni/android_media_MediaDrm.cpp
@@ -570,7 +570,7 @@
     FIND_CLASS(clazz, "android/media/MediaDrm$Certificate");
     GET_FIELD_ID(gFields.certificate.wrappedPrivateKey, clazz, "mWrappedKey", "[B");
     GET_FIELD_ID(gFields.certificate.certificateData, clazz, "mCertificateData", "[B");
-    gFields.certificateClassId = reinterpret_cast<jclass>(env->NewGlobalRef(clazz));
+    gFields.certificateClassId = static_cast<jclass>(env->NewGlobalRef(clazz));
 
     FIND_CLASS(clazz, "java/util/ArrayList");
     GET_METHOD_ID(gFields.arraylist.init, clazz, "<init>", "()V");
@@ -595,13 +595,13 @@
     GET_METHOD_ID(gFields.entry.getValue, clazz, "getValue", "()Ljava/lang/Object;");
 
     FIND_CLASS(clazz, "java/util/HashMap");
-    gFields.hashmapClassId = reinterpret_cast<jclass>(env->NewGlobalRef(clazz));
+    gFields.hashmapClassId = static_cast<jclass>(env->NewGlobalRef(clazz));
 
     FIND_CLASS(clazz, "java/lang/String");
-    gFields.stringClassId = reinterpret_cast<jclass>(env->NewGlobalRef(clazz));
+    gFields.stringClassId = static_cast<jclass>(env->NewGlobalRef(clazz));
 
     FIND_CLASS(clazz, "java/util/ArrayList");
-    gFields.arraylistClassId = reinterpret_cast<jclass>(env->NewGlobalRef(clazz));
+    gFields.arraylistClassId = static_cast<jclass>(env->NewGlobalRef(clazz));
 }
 
 static void android_media_MediaDrm_native_setup(