[LayoutNG] Add NGFragment class definition.

third_party/WebKit/Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 525 matching lines @@
             'layout/api/LineLayoutRubyRun.h',
             'layout/api/LineLayoutRubyText.h',
             'layout/api/LineLayoutSVGInline.h',
             'layout/api/LineLayoutSVGInlineText.h',
             'layout/api/LineLayoutSVGTextPath.h',
             'layout/api/LineLayoutText.h',
             'layout/api/LineLayoutTextCombine.h',
             'layout/api/SelectionState.h',
             'layout/ng/NGConstraintSpace.cpp',
             'layout/ng/NGConstraintSpace.h',
+            'layout/ng/NGFragment.cpp',
+            'layout/ng/NGFragment.h',
             'layout/BidiRun.h',
             'layout/BidiRunForLine.cpp',
             'layout/BidiRunForLine.h',
             'layout/ClipRect.cpp',
             'layout/ClipRect.h',
             'layout/ClipRects.h',
             'layout/ClipRectsCache.h',
             'layout/ColumnBalancer.cpp',
             'layout/ColumnBalancer.h',
             'layout/CounterNode.cpp',
@@ skipping 3685 matching lines @@
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'timing/PerformanceBaseTest.cpp',
             'timing/PerformanceObserverTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'workers/WorkerThreadTestHelper.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }