To ensure consistency between layouts, we need to reset any overriden top for centering the textfie…

Source/core/rendering/RenderTextControlSingleLine.cpp

 /**
  * Copyright (C) 2006, 2007, 2010 Apple Inc. All rights reserved.
  *           (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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 26 matching lines @@
 #include "platform/fonts/SimpleFontData.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 RenderTextControlSingleLine::RenderTextControlSingleLine(HTMLInputElement* element)
     : RenderTextControl(element)
     , m_shouldDrawCapsLockIndicator(false)
     , m_desiredInnerEditorLogicalHeight(-1)
+    , m_hasOverridenInnerEditorLogicalTop(false)
 {
 }
 
 RenderTextControlSingleLine::~RenderTextControlSingleLine()
 {
 }
 
 inline Element* RenderTextControlSingleLine::containerElement() const
 {
     return inputElement()->userAgentShadowRoot()->getElementById(ShadowElementNames::textFieldContainer());
@@ skipping 52 matching lines @@
     RenderBox* viewPortRenderer = editingViewPortElement() ? editingViewPortElement()->renderBox() : 0;
 
     // To ensure consistency between layouts, we need to reset any conditionally overriden height.
     if (innerEditorRenderer && !innerEditorRenderer->style()->logicalHeight().isAuto()) {
         innerEditorRenderer->style()->setLogicalHeight(Length(Auto));
         layoutScope.setNeedsLayout(innerEditorRenderer);
         HTMLElement* placeholderElement = inputElement()->placeholderElement();
         if (RenderBox* placeholderBox = placeholderElement ? placeholderElement->renderBox() : 0)
             layoutScope.setNeedsLayout(placeholderBox);
     }
+    if (m_hasOverridenInnerEditorLogicalTop) {
+        layoutScope.setNeedsLayout(innerEditorRenderer);
+        m_hasOverridenInnerEditorLogicalTop = false;
+    }
     if (viewPortRenderer && !viewPortRenderer->style()->logicalHeight().isAuto()) {
         viewPortRenderer->style()->setLogicalHeight(Length(Auto));
         layoutScope.setNeedsLayout(viewPortRenderer);
     }
 
     RenderBlockFlow::layoutBlock(false);
 
     Element* container = containerElement();
     RenderBox* containerRenderer = container ? container->renderBox() : 0;
 
@@ skipping 28 matching lines @@
     }
 
     // If we need another layout pass, we have changed one of children's height so we need to relayout them.
     if (needsLayout())
         RenderBlockFlow::layoutBlock(true);
 
     // Center the child block in the block progression direction (vertical centering for horizontal text fields).
     if (!container && innerEditorRenderer && innerEditorRenderer->height() != contentLogicalHeight()) {
         LayoutUnit logicalHeightDiff = innerEditorRenderer->logicalHeight() - contentLogicalHeight();
         innerEditorRenderer->setLogicalTop(innerEditorRenderer->logicalTop() - (logicalHeightDiff / 2 + layoutMod(logicalHeightDiff, 2)));
+        m_hasOverridenInnerEditorLogicalTop = true;
     } else
         centerContainerIfNeeded(containerRenderer);

[Julien - ping for review, 2014/11/19 01:13:27]

This also overrides the logical top under some conditions so shouldn't we set
the new boolean here too?

Overall this approach is not great: we prefer to check the previous layout's
values to determine if we need to do another layout or recompute extra
properties.

But more fundamentally, I think you're patching the problem, not the cause of
the problem. It seems like the formula to compute the logical top shouldn't use
a previous layout's information (if we end up not relaying
|innerEditorRenderer|). Forcing a layout forces the logical top to be reset,
which fixes the problem, but pays a high price for it by missing the root cause.

 
     HTMLElement* placeholderElement = inputElement()->placeholderElement();
     if (RenderBox* placeholderBox = placeholderElement ? placeholderElement->renderBox() : 0) {
         LayoutSize innerEditorSize;
 
         if (innerEditorRenderer)
             innerEditorSize = innerEditorRenderer->size();
         placeholderBox->style()->setWidth(Length(innerEditorSize.width() - placeholderBox->borderAndPaddingWidth(), Fixed));
         placeholderBox->style()->setHeight(Length(innerEditorSize.height() - placeholderBox->borderAndPaddingHeight(), Fixed));
         bool neededLayout = placeholderBox->needsLayout();
@@ skipping 233 matching lines @@
     if (innerEditorElement())
         innerEditorElement()->setScrollTop(newTop);
 }
 
 HTMLInputElement* RenderTextControlSingleLine::inputElement() const
 {
     return toHTMLInputElement(node());
 }
 
 }