Oilpan: Remove most WillBe types from the code base

third_party/WebKit/Source/modules/fetch/Body.h

Index: third_party/WebKit/Source/modules/fetch/Body.h
diff --git a/third_party/WebKit/Source/modules/fetch/Body.h b/third_party/WebKit/Source/modules/fetch/Body.h
index c13da67bedcfedf0a9b5a8264ba437b62596405c..200ab2b5e6cb20d5ee7e27bee97f3cf253eeb4fb 100644
--- a/third_party/WebKit/Source/modules/fetch/Body.h
+++ b/third_party/WebKit/Source/modules/fetch/Body.h
@@ -32,7 +32,7 @@ class MODULES_EXPORT Body
     , public ActiveDOMObject {
     WTF_MAKE_NONCOPYABLE(Body);
     DEFINE_WRAPPERTYPEINFO();
-    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(Body);
+    USING_GARBAGE_COLLECTED_MIXIN(Body);
 public:
     explicit Body(ExecutionContext*);
     ~Body() override { }