C++11: Replace 0 with nullptr where applicable in layout code.

Source/core/layout/svg/SVGTextMetrics.cpp

Index: Source/core/layout/svg/SVGTextMetrics.cpp
diff --git a/Source/core/layout/svg/SVGTextMetrics.cpp b/Source/core/layout/svg/SVGTextMetrics.cpp
index 63b48ce4672922bbf3b46951c797739f30930116..ebfd859af892863aa840d21f7b3b60ff96defe81 100644
--- a/Source/core/layout/svg/SVGTextMetrics.cpp
+++ b/Source/core/layout/svg/SVGTextMetrics.cpp
@@ -60,7 +60,7 @@ TextRun SVGTextMetrics::constructTextRun(LayoutSVGInlineText* text, unsigned pos
 {
     const ComputedStyle& style = text->styleRef();
 
-    TextRun run(static_cast<const LChar*>(0) // characters, will be set below if non-zero.
+    TextRun run(static_cast<const LChar*>(nullptr) // characters, will be set below if non-zero.
         , 0 // length, will be set below if non-zero.
         , 0 // xPos, only relevant with allowTabs=true
         , 0 // padding, only relevant for justified text, not relevant for SVG