[New Multicolumn] Let a spanner's containing block be the multicol container.

Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationNode.idl',
@@ skipping 1648 matching lines @@
             'rendering/RenderMediaControls.cpp',
             'rendering/RenderMediaControls.h',
             'rendering/RenderMenuList.cpp',
             'rendering/RenderMenuList.h',
             'rendering/RenderMeter.cpp',
             'rendering/RenderMeter.h',
             'rendering/RenderMultiColumnFlowThread.cpp',
             'rendering/RenderMultiColumnFlowThread.h',
             'rendering/RenderMultiColumnSet.cpp',
             'rendering/RenderMultiColumnSet.h',
-            'rendering/RenderMultiColumnSpannerSet.cpp',
-            'rendering/RenderMultiColumnSpannerSet.h',
+            'rendering/RenderMultiColumnSpannerPlaceholder.cpp',
+            'rendering/RenderMultiColumnSpannerPlaceholder.h',
             'rendering/RenderObject.cpp',
             'rendering/RenderObjectChildList.cpp',
             'rendering/RenderPagedFlowThread.cpp',
             'rendering/RenderPagedFlowThread.h',
             'rendering/RenderPart.cpp',
             'rendering/RenderProgress.cpp',
             'rendering/RenderProgress.h',
             'rendering/RenderQuote.cpp',
             'rendering/RenderQuote.h',
             'rendering/RenderRegion.cpp',
@@ skipping 1911 matching lines @@
             'rendering/style/OutlineValueTest.cpp',
             'rendering/style/RenderStyleTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }