CachedAppOptimizer: use new cgroup api for freezer path

Use the new cgroup API in place of the hardcoded path.
The new libprocessgroup API is defined in https://r.android.com/1607196

Bug: 180056337
Test: verified the freezer work via logs
Change-Id: I73c0976f3a917890bcd888c232975e2258f87b5c

services/core/jni/com_android_server_am_CachedAppOptimizer.cpp

@@ -280,7 +280,13 @@ static jint com_android_server_am_CachedAppOptimizer_getBinderFreezeInfo(JNIEnv
 
 static jstring com_android_server_am_CachedAppOptimizer_getFreezerCheckPath(JNIEnv* env,
                                                                             jobject clazz) {
-    return env->NewStringUTF(CGROUP_FREEZE_PATH);
+    std::string path;
+
+    if (!getAttributePathForTask("FreezerState", getpid(), &path)) {
+        path = "";
+    }
+
+    return env->NewStringUTF(path.c_str());
 }
 
 static const JNINativeMethod sMethods[] = {