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/paint/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("paint") {
   split_count = 2
   sources = [
     "BackgroundImageGeometry.cpp",
@@ skipping 86 matching lines @@
     "ObjectPaintProperties.h",
     "ObjectPainter.cpp",
     "ObjectPainter.h",
     "PaintInfo.cpp",
     "PaintInfo.h",
     "PaintInvalidationCapableScrollableArea.cpp",
     "PaintInvalidationCapableScrollableArea.h",
     "PaintInvalidator.cpp",
     "PaintInvalidator.h",
     "PaintLayer.cpp",
+    "PaintLayer.h",
     "PaintLayerClipper.cpp",
+    "PaintLayerClipper.h",
     "PaintLayerFragment.h",
     "PaintLayerPainter.cpp",
     "PaintLayerPainter.h",
     "PaintLayerPaintingInfo.h",
     "PaintLayerResourceInfo.cpp",
     "PaintLayerResourceInfo.h",
     "PaintLayerScrollableArea.cpp",
+    "PaintLayerScrollableArea.h",
     "PaintLayerStackingNode.cpp",
+    "PaintLayerStackingNode.h",
     "PaintLayerStackingNodeIterator.cpp",
+    "PaintLayerStackingNodeIterator.h",
     "PaintPhase.cpp",
     "PaintPhase.h",
     "PaintPropertyTreeBuilder.cpp",
     "PaintPropertyTreeBuilder.h",
     "PaintPropertyTreePrinter.cpp",
     "PaintPropertyTreePrinter.h",
     "PaintTiming.cpp",
     "PaintTiming.h",
     "PartPainter.cpp",
     "PartPainter.h",
@@ skipping 65 matching lines @@
     "ViewPaintInvalidator.h",
     "ViewPainter.cpp",
     "ViewPainter.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }