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/layout/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("layout") {
   split_count = 5
 
   sources = [
@@ skipping 14 matching lines @@
     "FragmentainerIterator.h",
     "FragmentationContext.h",
     "GeneratedChildren.h",
     "Grid.cpp",
     "Grid.h",
     "GridTrackSizingAlgorithm.cpp",
     "GridTrackSizingAlgorithm.h",
     "HitTestCache.cpp",
     "HitTestCache.h",
     "HitTestCanvasResult.cpp",
+    "HitTestCanvasResult.h",
     "HitTestLocation.cpp",
     "HitTestLocation.h",
     "HitTestResult.cpp",
     "HitTestingTransformState.cpp",
     "HitTestingTransformState.h",
     "ImageQualityController.cpp",
     "ImageQualityController.h",
     "IntersectionGeometry.cpp",
     "IntersectionGeometry.h",
     "LayoutAnalyzer.cpp",
     "LayoutAnalyzer.h",
     "LayoutBR.cpp",
     "LayoutBlock.cpp",
+    "LayoutBlock.h",
     "LayoutBlockFlow.cpp",
     "LayoutBlockFlowLine.cpp",
     "LayoutBox.cpp",
     "LayoutBoxModelObject.cpp",
+    "LayoutBoxModelObject.h",
     "LayoutButton.cpp",
     "LayoutButton.h",
     "LayoutCounter.cpp",
     "LayoutCounter.h",
     "LayoutDeprecatedFlexibleBox.cpp",
     "LayoutDeprecatedFlexibleBox.h",
     "LayoutDetailsMarker.cpp",
     "LayoutDetailsMarker.h",
     "LayoutEmbeddedObject.cpp",
+    "LayoutEmbeddedObject.h",
     "LayoutFieldset.cpp",
     "LayoutFieldset.h",
     "LayoutFileUploadControl.cpp",
     "LayoutFileUploadControl.h",
     "LayoutFlexibleBox.cpp",
     "LayoutFlexibleBox.h",
     "LayoutFlowThread.cpp",
     "LayoutFlowThread.h",
     "LayoutFrame.cpp",
     "LayoutFrame.h",
     "LayoutFrameSet.cpp",
     "LayoutFrameSet.h",
     "LayoutFullScreen.cpp",
     "LayoutFullScreen.h",
     "LayoutGeometryMap.cpp",
     "LayoutGeometryMap.h",
     "LayoutGeometryMapStep.h",
     "LayoutGrid.cpp",
     "LayoutGrid.h",
     "LayoutHTMLCanvas.cpp",
     "LayoutHTMLCanvas.h",
     "LayoutIFrame.cpp",
     "LayoutIFrame.h",
     "LayoutImage.cpp",
+    "LayoutImage.h",
     "LayoutImageResource.cpp",
+    "LayoutImageResource.h",
     "LayoutImageResourceStyleImage.cpp",
+    "LayoutImageResourceStyleImage.h",
     "LayoutInline.cpp",
     "LayoutInline.h",
     "LayoutListBox.cpp",
     "LayoutListBox.h",
     "LayoutListItem.cpp",
+    "LayoutListItem.h",
     "LayoutListMarker.cpp",
     "LayoutListMarker.h",
     "LayoutMedia.cpp",
     "LayoutMedia.h",
     "LayoutMenuList.cpp",
     "LayoutMenuList.h",
     "LayoutMultiColumnFlowThread.cpp",
     "LayoutMultiColumnFlowThread.h",
     "LayoutMultiColumnSet.cpp",
     "LayoutMultiColumnSet.h",
     "LayoutMultiColumnSpannerPlaceholder.cpp",
     "LayoutMultiColumnSpannerPlaceholder.h",
     "LayoutObject.cpp",
     "LayoutObjectChildList.cpp",
+    "LayoutObjectChildList.h",
     "LayoutPagedFlowThread.cpp",
     "LayoutPagedFlowThread.h",
     "LayoutPart.cpp",
+    "LayoutPart.h",
     "LayoutProgress.cpp",
     "LayoutProgress.h",
     "LayoutQuote.cpp",
     "LayoutQuote.h",
     "LayoutReplaced.cpp",
+    "LayoutReplaced.h",
     "LayoutRuby.cpp",
     "LayoutRuby.h",
     "LayoutRubyBase.cpp",
     "LayoutRubyBase.h",
     "LayoutRubyRun.cpp",
     "LayoutRubyRun.h",
     "LayoutRubyText.cpp",
     "LayoutRubyText.h",
     "LayoutScrollbar.cpp",
     "LayoutScrollbar.h",
     "LayoutScrollbarPart.cpp",
     "LayoutScrollbarPart.h",
     "LayoutScrollbarTheme.cpp",
     "LayoutScrollbarTheme.h",
     "LayoutSearchField.cpp",
     "LayoutSearchField.h",
     "LayoutSlider.cpp",
     "LayoutSlider.h",
     "LayoutSliderContainer.cpp",
     "LayoutSliderContainer.h",
     "LayoutSliderThumb.cpp",
     "LayoutSliderThumb.h",
     "LayoutState.cpp",
+    "LayoutState.h",
     "LayoutTable.cpp",
     "LayoutTable.h",
     "LayoutTableBoxComponent.cpp",
     "LayoutTableBoxComponent.h",
     "LayoutTableCaption.cpp",
     "LayoutTableCaption.h",
     "LayoutTableCell.cpp",
     "LayoutTableCell.h",
     "LayoutTableCol.cpp",
     "LayoutTableCol.h",
@@ skipping 23 matching lines @@
     "LayoutThemeMac.h",
     "LayoutThemeMac.mm",
     "LayoutThemeMobile.cpp",
     "LayoutThemeMobile.h",
     "LayoutTreeAsText.cpp",
     "LayoutVTTCue.cpp",
     "LayoutVTTCue.h",
     "LayoutVideo.cpp",
     "LayoutVideo.h",
     "LayoutView.cpp",
+    "LayoutView.h",
     "LayoutWordBreak.cpp",
     "LayoutWordBreak.h",
     "ListMarkerText.cpp",
     "ListMarkerText.h",
     "MultiColumnFragmentainerGroup.cpp",
     "MultiColumnFragmentainerGroup.h",
     "OrderIterator.cpp",
     "OrderIterator.h",
     "OverflowModel.h",
     "PaintInvalidationState.cpp",
     "PaintInvalidationState.h",
     "PointerEventsHitRules.cpp",
     "PointerEventsHitRules.h",
     "ScrollAlignment.cpp",
+    "ScrollAlignment.h",
     "ScrollAnchor.cpp",
     "ScrollAnchor.h",
     "SubtreeLayoutScope.cpp",
     "SubtreeLayoutScope.h",
     "TableLayoutAlgorithm.h",
     "TableLayoutAlgorithmAuto.cpp",
     "TableLayoutAlgorithmAuto.h",
     "TableLayoutAlgorithmFixed.cpp",
     "TableLayoutAlgorithmFixed.h",
     "TextAutosizer.cpp",
@@ skipping 63 matching lines @@
     "line/AbstractInlineTextBox.h",
     "line/BreakingContext.cpp",
     "line/EllipsisBox.cpp",
     "line/EllipsisBox.h",
     "line/GlyphOverflow.h",
     "line/InlineBox.cpp",
     "line/InlineFlowBox.cpp",
     "line/InlineIterator.h",
     "line/InlineTextBox.cpp",
     "line/LineBoxList.cpp",
+    "line/LineBoxList.h",
     "line/LineBreaker.cpp",
     "line/LineBreaker.h",
     "line/LineWidth.cpp",
     "line/LineWidth.h",
     "line/RootInlineBox.cpp",
     "line/TrailingObjects.cpp",
     "line/TrailingObjects.h",
     "ng/geometry/ng_box_strut.cc",
     "ng/geometry/ng_box_strut.h",
     "ng/geometry/ng_edge.h",
@@ skipping 124 matching lines @@
       "LayoutThemeAndroid.cpp",
       "LayoutThemeAndroid.h",
     ]
   }
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }