[layoutng] Add an NGFragmentBuilder

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/AnimationEffectReadOnly.idl',
             'animation/AnimationEffectTiming.idl',
@@ skipping 537 matching lines @@
             'layout/ng/ng_block_layout_algorithm.h',
             'layout/ng/ng_box.cc',
             'layout/ng/ng_box.h',
             'layout/ng/ng_box_iterator.cc',
             'layout/ng/ng_box_iterator.h',
             'layout/ng/ng_constraint_space.cc',
             'layout/ng/ng_constraint_space.h',
             'layout/ng/ng_derived_constraint_space.h',
             'layout/ng/ng_fragment_base.cc',
             'layout/ng/ng_fragment_base.h',
+            'layout/ng/ng_fragment_builder.cc',
+            'layout/ng/ng_fragment_builder.h',
             'layout/ng/ng_fragment.cc',
             'layout/ng/ng_fragment.h',
             'layout/ng/ng_layout_input_text.h',
             'layout/ng/ng_length_utils.cc',
             'layout/ng/ng_length_utils.h',
             'layout/ng/ng_margin_strut.h',
             'layout/ng/ng_text_fragment.cc',
             'layout/ng/ng_text_fragment.h',
             'layout/ng/ng_units.h',
             'layout/BidiRun.h',
@@ skipping 3726 matching lines @@
             'timing/MemoryInfoTest.cpp',
             'timing/PerformanceBaseTest.cpp',
             'timing/PerformanceObserverTest.cpp',
             'workers/DedicatedWorkerTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'workers/WorkerThreadTestHelper.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }