Bug 1230311 - add annotation to enforce that if a method is overridden also base method is called. r=nfroyd

MozReview-Commit-ID: AQ3Kx2qidU0

mfbt/Attributes.h

@@ -468,6 +468,10 @@
  *   use `auto` in place of this type in variable declarations.  This is intended to
  *   be used with types which are intended to be implicitly constructed into other
  *   other types before being assigned to variables.
+ * MOZ_REQUIRED_BASE_METHOD: Applies to virtual class method declarations.
+ *  Sometimes derived classes override methods that need to be called by their
+ *  overridden counterparts. This marker indicates that the marked method must
+ *  be called by the method that it overrides.
  */
 #ifdef MOZ_CLANG_PLUGIN
 #  define MOZ_MUST_OVERRIDE __attribute__((annotate("moz_must_override")))
@@ -501,6 +505,8 @@
     __attribute__((annotate("moz_ignore_ctor_initialization")))
 #  define MOZ_IS_CLASS_INIT \
     __attribute__((annotate("moz_is_class_init")))
+#  define MOZ_REQUIRED_BASE_METHOD \
+    __attribute__((annotate("moz_required_base_method")))
 /*
  * It turns out that clang doesn't like void func() __attribute__ {} without a
  * warning, so use pragmas to disable the warning. This code won't work on GCC
@@ -535,6 +541,7 @@
 #  define MOZ_INIT_OUTSIDE_CTOR /* nothing */
 #  define MOZ_IS_CLASS_INIT /* nothing */
 #  define MOZ_NON_AUTOABLE /* nothing */
+#  define MOZ_REQUIRED_BASE_METHOD /* nothing */
 #endif /* MOZ_CLANG_PLUGIN */
 
 #define MOZ_RAII MOZ_NON_TEMPORARY_CLASS MOZ_STACK_CLASS