[Layout API] Use layoutViewItem() in PaintLayer

Document::layoutView() is deprecated and being removed soon. The
replacement is Document::layoutViewItem(), which routes methods
through the new block layout API. No new API methods were required.

There are no functional changes.

BUG=499321

Review-Url: https://codereview.chromium.org/2146313003
Cr-Commit-Position: refs/heads/master@{#405586}

third_party/WebKit/Source/core/paint/PaintLayer.cpp

@@ -1601,7 +1601,7 @@ bool PaintLayer::hitTest(HitTestResult& result)
 
     // LayoutView should make sure to update layout before entering hit testing
     ASSERT(!layoutObject()->frame()->view()->layoutPending());
-    ASSERT(!layoutObject()->document().layoutView()->needsLayout());
+    ASSERT(!layoutObject()->document().layoutViewItem().needsLayout());
 
     const HitTestRequest& request = result.hitTestRequest();
     const HitTestLocation& hitTestLocation = result.hitTestLocation();