UseCounter: Introduce UseCounter::Observer for layout tests

third_party/WebKit/Source/core/testing/Internals.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 475 matching lines @@
   int visualViewportWidth();
   // The scroll position of the visual viewport relative to the document origin.
   float visualViewportScrollX();
   float visualViewportScrollY();
 
   // Return true if the given use counter exists for the given document.
   // |feature| must be one of the values from the UseCounter::Feature enum.
   bool isUseCounted(Document*, uint32_t feature);
   bool isCSSPropertyUseCounted(Document*, const String&);
 
+  // Observes changes on Document's UseCounter. Returns a promise that is
+  // resolved when |feature| is counted. When |feature| was already counted,
+  // it's immediately resolved.
+  ScriptPromise observeUseCounter(ScriptState*, Document*, uint32_t feature);
+
   // Used by the iterable<>.
   unsigned length() const { return 5; }
   int anonymousIndexedGetter(uint32_t index) const { return index * index; }
 
   String unscopableAttribute();
   String unscopableMethod();
 
   ClientRectList* focusRingRects(Element*);
   ClientRectList* outlineRects(Element*);
 
@@ skipping 37 matching lines @@
                            const String& markerType,
                            unsigned index,
                            ExceptionState&);
   Member<InternalRuntimeFlags> m_runtimeFlags;
   Member<Document> m_document;
 };
 
 }  // namespace blink
 
 #endif  // Internals_h