First step of PaintInvalidator implementation

third_party/WebKit/Source/core/paint/BlockFlowPaintInvalidator.cpp

Index: third_party/WebKit/Source/core/paint/BlockFlowPaintInvalidator.cpp
diff --git a/third_party/WebKit/Source/core/paint/BlockFlowPaintInvalidator.cpp b/third_party/WebKit/Source/core/paint/BlockFlowPaintInvalidator.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..b70c1f566968085122d73d5d3d6684cd6fcc6ffc
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/BlockFlowPaintInvalidator.cpp
@@ -0,0 +1,30 @@
+// Copyright 2016 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 "core/paint/BlockFlowPaintInvalidator.h"
+
+#include "core/layout/LayoutBlockFlow.h"
+#include "core/paint/BoxPaintInvalidator.h"
+#include "core/paint/PaintInvalidator.h"
+
+namespace blink {
+
+PaintInvalidationReason BlockFlowPaintInvalidator::invalidatePaintIfNeeded()
+{
+    PaintInvalidationReason reason = BoxPaintInvalidator(m_blockFlow, m_context).invalidatePaintIfNeeded();
+
+    if (reason == PaintInvalidationNone || reason == PaintInvalidationDelayedFull)
+        return reason;
+
+    RootInlineBox* line = m_blockFlow.firstRootBox();
+    if (line && line->isFirstLineStyle()) {
+        // It's the RootInlineBox that paints the ::first-line background. Note that since it may be
+        // expensive to figure out if the first line is affected by any ::first-line selectors at all,
+        // we just invalidate it unconditionally which is typically cheaper.
+        m_blockFlow.invalidateDisplayItemClient(*line, reason);
+    }
+    return reason;
+}
+
+} // namespace blink