IntersectionObserver: throw exceptions as spec mandates.

third_party/WebKit/Source/core/dom/IntersectionObserver.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IntersectionObserver_h
 #define IntersectionObserver_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/dom/IntersectionObservation.h"
 #include "core/dom/IntersectionObserverEntry.h"
@@ skipping 11 matching lines @@
 class IntersectionObserverInit;
 
 class CORE_EXPORT IntersectionObserver final : public GarbageCollectedFinalized<IntersectionObserver>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 
 public:
     static IntersectionObserver* create(const IntersectionObserverInit&, IntersectionObserverCallback&, ExceptionState&);
     static void resumeSuspendedObservers();
 
     // API methods
-    void observe(Element*);
-    void unobserve(Element*);
-    void disconnect();
-    HeapVector<Member<IntersectionObserverEntry>> takeRecords();
+    void observe(Element*, ExceptionState&);
+    void unobserve(Element*, ExceptionState&);
+    void disconnect(ExceptionState&);
+    HeapVector<Member<IntersectionObserverEntry>> takeRecords(ExceptionState&);
+
+    // API attributes
     Element* root() const;
     String rootMargin() const;
     const Vector<float>& thresholds() const { return m_thresholds; }
 
     Node* rootNode() const { return m_root.get(); }
     LayoutObject* rootLayoutObject() const;
     const Length& topMargin() const { return m_topMargin; }
     const Length& rightMargin() const { return m_rightMargin; }
     const Length& bottomMargin() const { return m_bottomMargin; }
     const Length& leftMargin() const { return m_leftMargin; }
@@ skipping 19 matching lines @@
     Vector<float> m_thresholds;
     Length m_topMargin;
     Length m_rightMargin;
     Length m_bottomMargin;
     Length m_leftMargin;
 };
 
 } // namespace blink
 
 #endif // IntersectionObserver_h