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

Index: third_party/WebKit/Source/core/loader/BUILD.gn
diff --git a/third_party/WebKit/Source/core/loader/BUILD.gn b/third_party/WebKit/Source/core/loader/BUILD.gn
index be697da6de3bdda25554010c6ec2f36e49bae092..e08b1f3b512ae389ec1113b08212010d264b3215 100644
--- a/third_party/WebKit/Source/core/loader/BUILD.gn
+++ b/third_party/WebKit/Source/core/loader/BUILD.gn
@@ -8,20 +8,26 @@ 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",
@@ -36,11 +42,13 @@ blink_core_sources("loader") {
     "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",