Inroduce toSVGInlineTextBox, and use it.

Source/core/rendering/svg/SVGInlineFlowBox.cpp

Index: Source/core/rendering/svg/SVGInlineFlowBox.cpp
diff --git a/Source/core/rendering/svg/SVGInlineFlowBox.cpp b/Source/core/rendering/svg/SVGInlineFlowBox.cpp
index 71303d6a418dfd45456810c5bac163478c7ae7b6..b93687ae0beb3f001b5f8dc7c44b519d52dddbb0 100644
--- a/Source/core/rendering/svg/SVGInlineFlowBox.cpp
+++ b/Source/core/rendering/svg/SVGInlineFlowBox.cpp
@@ -41,7 +41,7 @@ void SVGInlineFlowBox::paintSelectionBackground(PaintInfo& paintInfo)
     PaintInfo childPaintInfo(paintInfo);
     for (InlineBox* child = firstChild(); child; child = child->nextOnLine()) {
         if (child->isSVGInlineTextBox())
-            static_cast<SVGInlineTextBox*>(child)->paintSelectionBackground(childPaintInfo);
+            toSVGInlineTextBox(child)->paintSelectionBackground(childPaintInfo);
         else if (child->isSVGInlineFlowBox())
             static_cast<SVGInlineFlowBox*>(child)->paintSelectionBackground(childPaintInfo);
     }
@@ -59,7 +59,7 @@ void SVGInlineFlowBox::paint(PaintInfo& paintInfo, const LayoutPoint&, LayoutUni
     if (renderingContext.isRenderingPrepared()) {
         for (InlineBox* child = firstChild(); child; child = child->nextOnLine()) {
             if (child->isSVGInlineTextBox())
-                computeTextMatchMarkerRectForRenderer(toRenderSVGInlineText(static_cast<SVGInlineTextBox*>(child)->textRenderer()));
+                computeTextMatchMarkerRectForRenderer(toRenderSVGInlineText(toSVGInlineTextBox(child)->textRenderer()));
 
             child->paint(paintInfo, LayoutPoint(), 0, 0);
         }
@@ -105,7 +105,7 @@ void SVGInlineFlowBox::computeTextMatchMarkerRectForRenderer(RenderSVGInlineText
             if (!box->isSVGInlineTextBox())
                 continue;
 
-            SVGInlineTextBox* textBox = static_cast<SVGInlineTextBox*>(box);
+            SVGInlineTextBox* textBox = toSVGInlineTextBox(box);
 
             int markerStartPosition = max<int>(marker->startOffset() - textBox->start(), 0);
             int markerEndPosition = min<int>(marker->endOffset() - textBox->start(), textBox->len());