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

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

Index: third_party/WebKit/Source/modules/fetch/Headers.cpp
diff --git a/third_party/WebKit/Source/modules/fetch/Headers.cpp b/third_party/WebKit/Source/modules/fetch/Headers.cpp
index b8b6e61ab79bb9b484c61d15e1210ea3af77f9eb..d24a923dba09527f94d14c51bbdbf1d84a450dbe 100644
--- a/third_party/WebKit/Source/modules/fetch/Headers.cpp
+++ b/third_party/WebKit/Source/modules/fetch/Headers.cpp
@@ -59,16 +59,7 @@ Headers* Headers::Create(
   // "1. Let |headers| be a new Headers object whose guard is "none".
   Headers* headers = Create(exception_state);
   // "2. If |init| is given, fill headers with |init|. Rethrow any exception."
-  if (init.isByteStringSequenceSequence()) {
-    headers->FillWith(init.getAsByteStringSequenceSequence(), exception_state);
-  } else if (init.isByteStringByteStringRecord()) {
-    headers->FillWith(init.getAsByteStringByteStringRecord(), exception_state);
-  } else if (init.isHeaders()) {
-    // This branch will not be necessary once http://crbug.com/690428 is fixed.
-    headers->FillWith(init.getAsHeaders(), exception_state);
-  } else {
-    NOTREACHED();
-  }
+  headers->FillWith(init, exception_state);
   // "3. Return |headers|."
   return headers;
 }
@@ -243,6 +234,22 @@ void Headers::FillWith(const Headers* object, ExceptionState& exception_state) {
   }
 }
 
+void Headers::FillWith(
+    const ByteStringSequenceSequenceOrByteStringByteStringRecordOrHeaders& init,
+    ExceptionState& exception_state) {
+  DCHECK_EQ(header_list_->size(), 0U);
+  if (init.isByteStringSequenceSequence()) {
+    FillWith(init.getAsByteStringSequenceSequence(), exception_state);
+  } else if (init.isByteStringByteStringRecord()) {
+    FillWith(init.getAsByteStringByteStringRecord(), exception_state);
+  } else if (init.isHeaders()) {
+    // This branch will not be necessary once http://crbug.com/690428 is fixed.
+    FillWith(init.getAsHeaders(), exception_state);
+  } else {
+    NOTREACHED();
+  }
+}
+
 void Headers::FillWith(const Vector<Vector<String>>& object,
                        ExceptionState& exception_state) {
   DCHECK(!header_list_->size());