Remove diagnostic code from BlockPainter.

Source/core/paint/BlockPainter.cpp

Index: Source/core/paint/BlockPainter.cpp
diff --git a/Source/core/paint/BlockPainter.cpp b/Source/core/paint/BlockPainter.cpp
index 4fa00e8617878dcf7ad0e8c77acb4ff91b72e5ca..6e67e312828a2c9ef829db64e0046a269c8cecc6 100644
--- a/Source/core/paint/BlockPainter.cpp
+++ b/Source/core/paint/BlockPainter.cpp
@@ -36,14 +36,10 @@ void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOff
     // 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);