[New Multicolumn] Add support for column-span:all

Source/core/rendering/RenderMultiColumnSpannerPlaceholder.cpp

+// Copyright 2014 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.
+
+#include "config.h"
+
+#include "core/rendering/RenderMultiColumnSpannerPlaceholder.h"
+
+#include "core/rendering/RenderMultiColumnFlowThread.h"
+
+namespace blink {
+
+RenderMultiColumnSpannerPlaceholder* RenderMultiColumnSpannerPlaceholder::createAnonymous(RenderMultiColumnFlowThread* flowThread, RenderBox* spanner, RenderStyle* parentStyle)
+{
+    RenderMultiColumnSpannerPlaceholder* renderer = new RenderMultiColumnSpannerPlaceholder(flowThread, spanner);
+    renderer->setDocumentForAnonymous(&flowThread->document());
+    RefPtr<RenderStyle> newStyle(RenderStyle::createAnonymousStyleWithDisplay(parentStyle, BLOCK));
+
+    // We don't want floats in the row preceding the spanner to continue on the other side.
+    newStyle->setClear(CBOTH);
+
+    // A spanner must be padded with a pagination strut, so that contents that come after the
+    // spanner don't bleed into the column preceding the spanner.
+    newStyle->setColumnBreakBefore(PBALWAYS);
+
+    renderer->setStyle(newStyle.release());
+    return renderer;
+}
+
+RenderMultiColumnSpannerPlaceholder::RenderMultiColumnSpannerPlaceholder(RenderMultiColumnFlowThread* flowThread, RenderBox* spanner)
+    : RenderBox(0)
+    , m_flowThread(flowThread)
+    , m_spanner(spanner)
+{
+}
+
+void RenderMultiColumnSpannerPlaceholder::markForPaginationRelayoutIfNeeded(SubtreeLayoutScope& layoutScope)
+{
+    // Cannot skip spanner placeholder layout. We need to enter in order to advance to the column
+    // set following the spanner.
+    layoutScope.setChildNeedsLayout(this);
+}
+
+void RenderMultiColumnSpannerPlaceholder::layout()
+{
+    RenderBox::layout();
+    m_flowThread->advanceToNextColumnSet(this);
+}
+
+const char* RenderMultiColumnSpannerPlaceholder::renderName() const
+{
+    return "RenderMultiColumnSpannerPlaceholder";
+}
+
+} // namespace blink