Revert Enable new multicol for testing and experimental web platform features.

Source/core/layout/LayoutTestHelper.cpp

Index: Source/core/layout/LayoutTestHelper.cpp
diff --git a/Source/core/layout/LayoutTestHelper.cpp b/Source/core/layout/LayoutTestHelper.cpp
index 8723df463566030ae4b6ad85f048c0348658be1a..4055ce53d74d23d4cc9b846cb4b03eeb3a44893a 100644
--- a/Source/core/layout/LayoutTestHelper.cpp
+++ b/Source/core/layout/LayoutTestHelper.cpp
@@ -35,6 +35,8 @@ void RenderingTest::SetUp()
     m_pageClients.chromeClient = chromeClient;
     m_pageHolder = DummyPageHolder::create(IntSize(800, 600), &m_pageClients);
 
+    document().settings()->setRegionBasedColumnsEnabled(true);
+
     // This ensures that the minimal DOM tree gets attached
     // correctly for tests that don't call setBodyInnerHTML.
     document().view()->updateLayoutAndStyleIfNeededRecursive();