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

third_party/WebKit/Source/core/loader/BUILD.gn

 # Copyright 2016 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("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("loader") {
   sources = [
     "CookieJar.cpp",
     "DocumentLoadTiming.cpp",
+    "DocumentLoadTiming.h",
     "DocumentLoader.cpp",
+    "DocumentLoader.h",
     "DocumentThreadableLoader.cpp",
     "DocumentThreadableLoader.h",
     "DocumentThreadableLoaderClient.h",
     "DocumentWriter.cpp",
+    "DocumentWriter.h",
     "EmptyClients.cpp",
     "EmptyClients.h",
     "FormSubmission.cpp",
+    "FormSubmission.h",
     "FrameFetchContext.cpp",
     "FrameFetchContext.h",
     "FrameLoadRequest.cpp",
     "FrameLoadRequest.h",
     "FrameLoader.cpp",
+    "FrameLoader.h",
     "FrameLoaderStateMachine.cpp",
+    "FrameLoaderStateMachine.h",
     "HistoryItem.cpp",
     "HistoryItem.h",
     "HttpEquiv.cpp",
     "HttpEquiv.h",
     "ImageLoader.cpp",
     "ImageLoader.h",
     "LinkLoader.cpp",
     "LinkLoader.h",
     "LinkLoaderClient.h",
     "MixedContentChecker.cpp",
     "MixedContentChecker.h",
     "NavigationPolicy.cpp",
     "NavigationPolicy.h",
     "NavigationScheduler.cpp",
+    "NavigationScheduler.h",
     "PingLoader.cpp",
     "PingLoader.h",
     "PrerendererClient.cpp",
     "PrerendererClient.h",
     "ProgressTracker.cpp",
+    "ProgressTracker.h",
     "SubresourceFilter.cpp",
     "SubresourceFilter.h",
     "TextResourceDecoderBuilder.cpp",
     "TextResourceDecoderBuilder.h",
     "TextTrackLoader.cpp",
     "TextTrackLoader.h",
     "ThreadableLoader.cpp",
     "ThreadableLoaderClient.h",
     "ThreadableLoadingContext.cpp",
     "ThreadableLoadingContext.h",
@@ skipping 43 matching lines @@
     "resource/TextResource.h",
     "resource/XSLStyleSheetResource.cpp",
     "resource/XSLStyleSheetResource.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }