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

third_party/WebKit/Source/platform/wtf/BUILD.gn

 # Copyright 2017 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.
 
 # The below is a temporary setup during the WTF migration project:
 # https://groups.google.com/a/chromium.org/d/msg/blink-dev/tLdAZCTlcAA/bYXVT8gYCAAJ
 #
 # We are moving wtf/ files to platform/wtf/ incrementally, thus, conceptually,
 # the "wtf" target in wtf/BUILD.gn is being split into two, in a way that
 # only wtf/ can refer the contents in platform/wtf/.
@@ skipping 175 matching lines @@
     "text/StringConcatenate.h",
     "text/StringHash.h",
     "text/StringImpl.cpp",
     "text/StringImpl.h",
     "text/StringImplCF.cpp",
     "text/StringImplMac.mm",
     "text/StringMac.mm",
     "text/StringOperators.h",
     "text/StringStatics.cpp",
     "text/StringStatics.h",
+    "text/StringStatics.h",
     "text/StringToNumber.cpp",
     "text/StringToNumber.h",
     "text/StringUTF8Adaptor.h",
     "text/StringView.cpp",
     "text/StringView.h",
     "text/TextCodec.cpp",
     "text/TextCodec.h",
     "text/TextCodecASCIIFastPath.h",
     "text/TextCodecICU.cpp",
     "text/TextCodecICU.h",
+    "text/TextCodecICU.h",
     "text/TextCodecLatin1.cpp",
     "text/TextCodecLatin1.h",
+    "text/TextCodecLatin1.h",
     "text/TextCodecReplacement.cpp",
     "text/TextCodecReplacement.h",
     "text/TextCodecUTF16.cpp",
     "text/TextCodecUTF16.h",
+    "text/TextCodecUTF16.h",
     "text/TextCodecUTF8.cpp",
     "text/TextCodecUTF8.h",
     "text/TextCodecUserDefined.cpp",
     "text/TextCodecUserDefined.h",
+    "text/TextCodecUserDefined.h",
     "text/TextEncoding.cpp",
     "text/TextEncoding.h",
+    "text/TextEncoding.h",
     "text/TextEncodingRegistry.cpp",
     "text/TextEncodingRegistry.h",
+    "text/TextEncodingRegistry.h",
     "text/TextPosition.cpp",
     "text/TextPosition.h",
     "text/UTF8.cpp",
     "text/UTF8.h",
     "text/Unicode.h",
     "text/WTFString.cpp",
     "text/WTFString.h",
     "text/icu/CollatorICU.cpp",
     "text/icu/UnicodeIcu.h",
   ]
@@ skipping 51 matching lines @@
       "text/AtomicStringCF.cpp",
       "text/StringImplCF.cpp",
     ]
   }
 
   if (remove_webcore_debug_symbols) {
     configs -= [ "//build/config/compiler:default_symbols" ]
     configs += [ "//build/config/compiler:no_symbols" ]
   }
 }