init: Document the locking strategy used in class PropWaiterState

Let the compiler verify that lock_ is held when any of the data members
are accessed.

Bug: 266255006
Change-Id: I71b341815d84ab530627d934ad4d4681b652b9d8
Signed-off-by: Bart Van Assche <bvanassche@google.com>
diff --git a/init/init.cpp b/init/init.cpp
index 9312f26..c965fe6 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -212,16 +212,16 @@
     }
 
   private:
-    void ResetWaitForPropLocked() {
+    void ResetWaitForPropLocked() EXCLUSIVE_LOCKS_REQUIRED(lock_) {
         wait_prop_name_.clear();
         wait_prop_value_.clear();
         waiting_for_prop_.reset();
     }
 
     std::mutex lock_;
-    std::unique_ptr<Timer> waiting_for_prop_{nullptr};
-    std::string wait_prop_name_;
-    std::string wait_prop_value_;
+    GUARDED_BY(lock_) std::unique_ptr<Timer> waiting_for_prop_{nullptr};
+    GUARDED_BY(lock_) std::string wait_prop_name_;
+    GUARDED_BY(lock_) std::string wait_prop_value_;
 
 } prop_waiter_state;