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

Source/core/layout/LayoutTextControl.cpp

Index: Source/core/layout/LayoutTextControl.cpp
diff --git a/Source/core/layout/LayoutTextControl.cpp b/Source/core/layout/LayoutTextControl.cpp
index 13904a336824283981bf8b5a9fe6b7d45a4dda10..dead442420d4f8010f75412b453efa9d25d37207 100644
--- a/Source/core/layout/LayoutTextControl.cpp
+++ b/Source/core/layout/LayoutTextControl.cpp
@@ -205,7 +205,7 @@ static const char* const fontFamiliesWithInvalidCharWidth[] = {
 // all platforms.
 bool LayoutTextControl::hasValidAvgCharWidth(AtomicString family)
 {
-    static HashSet<AtomicString>* fontFamiliesWithInvalidCharWidthMap = 0;
+    static HashSet<AtomicString>* fontFamiliesWithInvalidCharWidthMap = nullptr;
 
     if (family.isEmpty())
         return false;
@@ -290,9 +290,9 @@ void LayoutTextControl::addFocusRingRects(Vector<LayoutRect>& rects, const Layou
 LayoutObject* LayoutTextControl::layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
 {
     HTMLElement* placeholder = toHTMLTextFormControlElement(node())->placeholderElement();
-    LayoutObject* placeholderLayoutObject = placeholder ? placeholder->layoutObject() : 0;
+    LayoutObject* placeholderLayoutObject = placeholder ? placeholder->layoutObject() : nullptr;
     if (!placeholderLayoutObject)
-        return 0;
+        return nullptr;
     if (relayoutChildren)
         layoutScope.setChildNeedsLayout(placeholderLayoutObject);
     return placeholderLayoutObject;