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

Source/core/layout/LayoutVideo.cpp

Index: Source/core/layout/LayoutVideo.cpp
diff --git a/Source/core/layout/LayoutVideo.cpp b/Source/core/layout/LayoutVideo.cpp
index dfcde4d4f1efc6dd0b2c5c986a38be55adf94bb6..409a9b97a842c3416d70f4722b396b55fbb92b13 100644
--- a/Source/core/layout/LayoutVideo.cpp
+++ b/Source/core/layout/LayoutVideo.cpp
@@ -126,7 +126,7 @@ void LayoutVideo::imageChanged(WrappedImagePtr newImage, const IntRect* rect)
 
 IntRect LayoutVideo::videoBox() const
 {
-    const LayoutSize* overriddenIntrinsicSize = 0;
+    const LayoutSize* overriddenIntrinsicSize = nullptr;
     if (videoElement()->shouldDisplayPosterImage())
         overriddenIntrinsicSize = &m_cachedImageSize;
 
@@ -204,11 +204,11 @@ static const LayoutBlock* layoutObjectPlaceholder(const LayoutObject* layoutObje
 {
     LayoutObject* parent = layoutObject->parent();
     if (!parent)
-        return 0;
+        return nullptr;
 
     LayoutFullScreen* fullScreen = parent->isLayoutFullScreen() ? toLayoutFullScreen(parent) : 0;
     if (!fullScreen)
-        return 0;
+        return nullptr;
 
     return fullScreen->placeholder();
 }