Remove diagnostic code from BlockPainter.

Source/core/paint/BlockPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/BlockPainter.h"
 
 #include "core/editing/FrameSelection.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutFlexibleBox.h"
@@ skipping 18 matching lines @@
 {
     PaintInfo localPaintInfo(paintInfo);
 
     LayoutPoint adjustedPaintOffset = paintOffset + m_layoutBlock.location();
 
     PaintPhase originalPhase = localPaintInfo.phase;
 
     // Check if we need to do anything at all.
     // FIXME: Could eliminate the isDocumentElement() check if we fix background painting so that the LayoutView
     // paints the root's background.
-    // TODO(schenney): Unroll m_layoutBlock.isDocumentElement() to try to get some insight into crbug.com/475698
     Node* blockNode = m_layoutBlock.node();
     RELEASE_ASSERT(blockNode || m_layoutBlock.isAnonymous());
     if (blockNode) {
-        TreeScope& blockTreescope = blockNode->treeScope(); // Will crash on bad node
-        Document& blockDocument = blockTreescope.document(); // Will crash in bad treeScope
-        Element* blockDocumentElement = blockDocument.documentElement(); // Will crash on bad TreeScope::m_document
-        if (blockDocumentElement != blockNode) {
+        if (m_layoutBlock.isDocumentElement()) {

[chrishtr, 2015/07/13 17:09:40]

I think this conditional needs to be inverted. It appears to have caused the
performance regression in crbug.com/504955.

[Stephen Chennney, 2015/07/20 17:42:30]

Can't believe I messed this up, and nothing broke is even more unbelievable.
https://codereview.chromium.org/1219093002/

             LayoutRect overflowBox = overflowRectForPaintRejection();
             m_layoutBlock.flipForWritingMode(overflowBox);
             overflowBox.moveBy(adjustedPaintOffset);
             if (!overflowBox.intersects(LayoutRect(localPaintInfo.rect)))
                 return;
         }
     } else {
         RELEASE_ASSERT(!m_layoutBlock.isDocumentElement());
     }
 
@@ skipping 290 matching lines @@
         LayoutBlock* block = flow->containingBlock();
         for ( ; block && block != &m_layoutBlock; block = block->containingBlock())
             accumulatedPaintOffset.moveBy(block->location());
         ASSERT(block);
         InlinePainter(*flow).paintOutline(info, accumulatedPaintOffset);
     }
 }
 
 
 } // namespace blink