Have Node::document() return a reference instead of a pointer

Source/core/css/resolver/StyleAdjuster.cpp

Index: Source/core/css/resolver/StyleAdjuster.cpp
diff --git a/Source/core/css/resolver/StyleAdjuster.cpp b/Source/core/css/resolver/StyleAdjuster.cpp
index ebc03ca2be584f787c2cd0c19463ec5a0cbef0fe..cb66e27a22e9234710cc937a8164b5d70c4a672a 100644
--- a/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/Source/core/css/resolver/StyleAdjuster.cpp
@@ -222,7 +222,7 @@ void StyleAdjuster::adjustRenderStyle(RenderStyle* style, RenderStyle* parentSty
             style->setPosition(AbsolutePosition);
 
         // Absolute/fixed positioned elements, floating elements and the document element need block-like outside display.
-        if (style->hasOutOfFlowPosition() || style->isFloating() || (e && e->document()->documentElement() == e))
+        if (style->hasOutOfFlowPosition() || style->isFloating() || (e && e->document().documentElement() == e))
             style->setDisplay(equivalentBlockDisplay(style->display(), style->isFloating(), !m_useQuirksModeStyles));
 
         // FIXME: Don't support this mutation for pseudo styles like first-letter or first-line, since it's not completely
@@ -264,7 +264,7 @@ void StyleAdjuster::adjustRenderStyle(RenderStyle* style, RenderStyle* parentSty
     // Auto z-index becomes 0 for the root element and transparent objects. This prevents
     // cases where objects that should be blended as a single unit end up with a non-transparent
     // object wedged in between them. Auto z-index also becomes 0 for objects that specify transforms/masks/reflections.
-    if (style->hasAutoZIndex() && ((e && e->document()->documentElement() == e)
+    if (style->hasAutoZIndex() && ((e && e->document().documentElement() == e)
         || style->opacity() < 1.0f
         || style->hasTransformRelatedProperty()
         || style->hasMask()
@@ -273,7 +273,7 @@ void StyleAdjuster::adjustRenderStyle(RenderStyle* style, RenderStyle* parentSty
         || style->hasFilter()
         || style->hasBlendMode()
         || style->position() == StickyPosition
-        || (style->position() == FixedPosition && e && e->document()->page() && e->document()->page()->settings().fixedPositionCreatesStackingContext())
+        || (style->position() == FixedPosition && e && e->document().page() && e->document().page()->settings().fixedPositionCreatesStackingContext())
         || isInTopLayer(e, style)
         ))
         style->setZIndex(0);