fetch: Align RequestInit's |headers| with the spec.

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

Index: third_party/WebKit/Source/modules/fetch/Headers.h
diff --git a/third_party/WebKit/Source/modules/fetch/Headers.h b/third_party/WebKit/Source/modules/fetch/Headers.h
index de5ffab206b723d49c0ca457c72beaa2148233a4..125c523ef95180718a8ab1d29f8cc6dfba3c20f5 100644
--- a/third_party/WebKit/Source/modules/fetch/Headers.h
+++ b/third_party/WebKit/Source/modules/fetch/Headers.h
@@ -17,6 +17,9 @@ namespace blink {
 class ByteStringSequenceSequenceOrByteStringByteStringRecordOrHeaders;
 class ExceptionState;
 
+using HeadersInit =
+    ByteStringSequenceSequenceOrByteStringByteStringRecordOrHeaders;
+
 // http://fetch.spec.whatwg.org/#headers-class
 class MODULES_EXPORT Headers final : public GarbageCollected<Headers>,
                                      public ScriptWrappable,
@@ -33,9 +36,7 @@ class MODULES_EXPORT Headers final : public GarbageCollected<Headers>,
   };
 
   static Headers* Create(ExceptionState&);
-  static Headers* Create(
-      const ByteStringSequenceSequenceOrByteStringByteStringRecordOrHeaders&,
-      ExceptionState&);
+  static Headers* Create(const HeadersInit&, ExceptionState&);
 
   // Shares the FetchHeaderList. Called when creating a Request or Response.
   static Headers* Create(FetchHeaderList*);
@@ -54,8 +55,7 @@ class MODULES_EXPORT Headers final : public GarbageCollected<Headers>,
 
   // These methods should only be called when size() would return 0.
   void FillWith(const Headers*, ExceptionState&);
-  void FillWith(const Vector<Vector<String>>&, ExceptionState&);
-  void FillWith(const Vector<std::pair<String, String>>&, ExceptionState&);
+  void FillWith(const HeadersInit&, ExceptionState&);
 
   FetchHeaderList* HeaderList() const { return header_list_; }
   DECLARE_TRACE();
@@ -65,6 +65,10 @@ class MODULES_EXPORT Headers final : public GarbageCollected<Headers>,
   // Shares the FetchHeaderList. Called when creating a Request or Response.
   explicit Headers(FetchHeaderList*);
 
+  // These methods should only be called when size() would return 0.
+  void FillWith(const Vector<Vector<String>>&, ExceptionState&);
+  void FillWith(const Vector<std::pair<String, String>>&, ExceptionState&);
+
   Member<FetchHeaderList> header_list_;
   Guard guard_;