HTTPHeaderMap: Favor composition over inheritance.

Source/platform/network/HTTPHeaderMap.h

Index: Source/platform/network/HTTPHeaderMap.h
diff --git a/Source/platform/network/HTTPHeaderMap.h b/Source/platform/network/HTTPHeaderMap.h
index 811a40de644df9a07e60ffc8ed31d07ab2c1bd22..f18cec05bd778e4e9dfc46a7482781a3ae7a97e0 100644
--- a/Source/platform/network/HTTPHeaderMap.h
+++ b/Source/platform/network/HTTPHeaderMap.h
@@ -41,7 +41,7 @@ namespace blink {
 typedef Vector<std::pair<String, String> > CrossThreadHTTPHeaderMapData;
 
 // FIXME: Not every header fits into a map. Notably, multiple Set-Cookie header fields are needed to set multiple cookies.
-class PLATFORM_EXPORT HTTPHeaderMap : public HashMap<AtomicString, AtomicString, CaseFoldingHash> {
+class PLATFORM_EXPORT HTTPHeaderMap {
 public:
     HTTPHeaderMap();
     ~HTTPHeaderMap();
@@ -51,15 +51,28 @@ public:
 
     void adopt(PassOwnPtr<CrossThreadHTTPHeaderMapData>);
 
-    const AtomicString& get(const AtomicString& name) const;
+    typedef HashMap<AtomicString, AtomicString, CaseFoldingHash> MapType;
+    typedef MapType::AddResult AddResult;
+    typedef MapType::const_iterator const_iterator;
 
-    AddResult add(const AtomicString& name, const AtomicString& value);
+    size_t size() const { return m_headers.size(); }
+    const_iterator begin() const { return m_headers.begin(); }
+    const_iterator end() const { return m_headers.end(); }
+    const_iterator find(const AtomicString &k) const { return m_headers.find(k); }
+    void clear() { m_headers.clear(); }
+    const AtomicString& get(const AtomicString& k) const { return m_headers.get(k); }
+    AddResult set(const AtomicString& k, const AtomicString& v) { return m_headers.set(k, v); }
+    AddResult add(const AtomicString& k, const AtomicString& v) { return m_headers.add(k, v); }
+    void remove(const AtomicString& k) { m_headers.remove(k); }
+    bool operator!=(const HTTPHeaderMap &rhs) const { return m_headers != rhs.m_headers; }
 
     // Alternate accessors that are faster than converting the char* to AtomicString first.
     bool contains(const char*) const;
     const AtomicString& get(const char*) const;
     AddResult add(const char* name, const AtomicString& value);
 
+private:
+    HashMap<AtomicString, AtomicString, CaseFoldingHash> m_headers;
 };
 
 } // namespace blink