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 01dfe881df248a165f6a5767ef30d2820fd3b56c..79064d06161d044025c1745a1e77fe8cd2ebf835 100644
--- a/third_party/WebKit/Source/modules/fetch/Body.h
+++ b/third_party/WebKit/Source/modules/fetch/Body.h
@@ -34,7 +34,7 @@ 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 { }