Add missing .h files to .gn files that have a .cc file next to it in the gn file already.

third_party/WebKit/Source/modules/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/split_static_library.gni")
 import("//build/config/chromecast_build.gni")
 import("//third_party/WebKit/Source/bindings/bindings.gni")
 import("//third_party/WebKit/Source/bindings/modules/v8/generated.gni")
 import("//third_party/WebKit/Source/bindings/modules/v8/v8.gni")
 import("//third_party/WebKit/Source/build/scripts/scripts.gni")
@@ skipping 233 matching lines @@
     "credentialmanager/PasswordCredentialTest.cpp",
     "csspaint/PaintRenderingContext2DTest.cpp",
     "csspaint/PaintWorkletTest.cpp",
     "document_metadata/CopylessPasteExtractorTest.cpp",
     "eventsource/EventSourceParserTest.cpp",
     "fetch/BlobBytesConsumerTest.cpp",
     "fetch/BodyStreamBufferTest.cpp",
     "fetch/BytesConsumerForDataConsumerHandleTest.cpp",
     "fetch/BytesConsumerTest.cpp",
     "fetch/BytesConsumerTestUtil.cpp",
+    "fetch/BytesConsumerTestUtil.h",
     "fetch/DataConsumerHandleTestUtil.cpp",
     "fetch/DataConsumerHandleTestUtil.h",
     "fetch/FetchDataLoaderTest.cpp",
     "fetch/FetchResponseDataTest.cpp",
     "fetch/FormDataBytesConsumerTest.cpp",
     "fetch/ReadableStreamBytesConsumerTest.cpp",
     "fetch/RequestTest.cpp",
     "fetch/ResponseTest.cpp",
     "filesystem/DOMFileSystemBaseTest.cpp",
     "indexeddb/IDBKeyPathTest.cpp",
@@ skipping 51 matching lines @@
     ":modules_testing",
     "//components/payments/content:payment_request_blink",
     "//skia",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/WebKit/Source/core",
     "//third_party/WebKit/Source/wtf",
     "//v8",
   ]
 }