Renderer.LineLayoutMs UMA histogram to measure line layout time.

Source/core/rendering/RenderBlockLineLayout.cpp

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All right reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 749 matching lines @@
             if (!lastObject->isBR())
                 lastObject = &lastRootBox()->firstLeafChild()->renderer();
             if (lastObject->isBR()) {
                 EClear clear = lastObject->style()->clear();
                 if (clear != CNONE)
                     clearFloats(clear);
             }
         }
     }
 
+    double start = WTF::currentTimeMS();
     layoutRunsAndFloatsInRange(layoutState, resolver, cleanLineStart, cleanLineBidiStatus);
+    frameView()->lineLayoutTime(WTF::currentTimeMS() - start);
     linkToEndLineIfNeeded(layoutState);
     markDirtyFloatsForPaintInvalidation(layoutState.floats());
 }
 
 // Before restarting the layout loop with a new logicalHeight, remove all floats that were added and reset the resolver.
 inline const InlineIterator& RenderBlockFlow::restartLayoutRunsAndFloatsInRange(LayoutUnit oldLogicalHeight, LayoutUnit newLogicalHeight,  FloatingObject* lastFloatFromPreviousLine, InlineBidiResolver& resolver,  const InlineIterator& oldEnd)
 {
     removeFloatingObjectsBelow(lastFloatFromPreviousLine, oldLogicalHeight);
     setLogicalHeight(newLogicalHeight);
     resolver.setPositionIgnoringNestedIsolates(oldEnd);
@@ skipping 1267 matching lines @@
     float logicalLeft = logicalLeftOffsetForLine(logicalHeight(), false).toFloat();
     float availableLogicalWidth = logicalRightOffsetForLine(logicalHeight(), false) - logicalLeft;
     updateLogicalWidthForAlignment(textAlign, 0, 0, logicalLeft, totalLogicalWidth, availableLogicalWidth, 0);
 
     if (!style()->isLeftToRightDirection())
         return logicalWidth() - logicalLeft;
     return logicalLeft;
 }
 
 }