Fetch: Make Headers' constructor match the current spec IDL.

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

Index: third_party/WebKit/Source/modules/fetch/RequestInit.cpp
diff --git a/third_party/WebKit/Source/modules/fetch/RequestInit.cpp b/third_party/WebKit/Source/modules/fetch/RequestInit.cpp
index 54a76a215bdb1497bd74102830eef4e701a0dc90..b892ca9071dbb80a5f5d732fe0c05063c5b1cab6 100644
--- a/third_party/WebKit/Source/modules/fetch/RequestInit.cpp
+++ b/third_party/WebKit/Source/modules/fetch/RequestInit.cpp
@@ -11,6 +11,7 @@
 #include "bindings/core/v8/V8Blob.h"
 #include "bindings/core/v8/V8FormData.h"
 #include "bindings/core/v8/V8URLSearchParams.h"
+#include "bindings/modules/v8/ByteStringSequenceSequenceOrDictionaryOrHeaders.h"
 #include "bindings/modules/v8/V8PasswordCredential.h"
 #include "core/dom/URLSearchParams.h"
 #include "core/fileapi/Blob.h"
@@ -30,18 +31,11 @@ RequestInit::RequestInit(ExecutionContext* context,
                          ExceptionState& exceptionState)
     : areAnyMembersSet(false) {
   areAnyMembersSet |= DictionaryHelper::get(options, "method", method);
-  areAnyMembersSet |= DictionaryHelper::get(options, "headers", headers);
-  if (!headers) {
-    Vector<Vector<String>> headersVector;
-    if (DictionaryHelper::get(options, "headers", headersVector,
-                              exceptionState)) {
-      headers = Headers::create(headersVector, exceptionState);
-      areAnyMembersSet = true;
-    } else {
-      areAnyMembersSet |=
-          DictionaryHelper::get(options, "headers", headersDictionary);
-    }
-  }
+
+  v8::Local<v8::Value> v8Headers;
+  bool isHeadersSet = DictionaryHelper::get(options, "headers", v8Headers);
+  areAnyMembersSet |= isHeadersSet;
+
   areAnyMembersSet |= DictionaryHelper::get(options, "mode", mode);
   areAnyMembersSet |= DictionaryHelper::get(options, "redirect", redirect);
   AtomicString referrerString;
@@ -99,6 +93,15 @@ RequestInit::RequestInit(ExecutionContext* context,
   }
 
   v8::Isolate* isolate = toIsolate(context);
+
+  if (isHeadersSet) {
+    ByteStringSequenceSequenceOrDictionaryOrHeaders headersInit;
+    V8ByteStringSequenceSequenceOrDictionaryOrHeaders::toImpl(
+        isolate, v8Headers, headersInit, UnionTypeConversionMode::NotNullable,
+        exceptionState);
+    headers = Headers::create(headersInit, exceptionState);
+  }
+
   if (isCredentialSet) {
     if (V8PasswordCredential::hasInstance(v8Credential, isolate)) {
       // TODO(mkwst): According to the spec, we'd serialize this once we touch