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

Source/core/rendering/RenderTextControlSingleLine.cpp

Index: Source/core/rendering/RenderTextControlSingleLine.cpp
diff --git a/Source/core/rendering/RenderTextControlSingleLine.cpp b/Source/core/rendering/RenderTextControlSingleLine.cpp
index 8d2c0453ee84921291a6775c16ee1eaa2e030c39..ca3f408153ff500429333952cf60bebd880d25ad 100644
--- a/Source/core/rendering/RenderTextControlSingleLine.cpp
+++ b/Source/core/rendering/RenderTextControlSingleLine.cpp
@@ -44,6 +44,7 @@ RenderTextControlSingleLine::RenderTextControlSingleLine(HTMLInputElement* eleme
     : RenderTextControl(element)
     , m_shouldDrawCapsLockIndicator(false)
     , m_desiredInnerEditorLogicalHeight(-1)
+    , m_hasOverridenInnerEditorLogicalTop(false)
 {
 }
 
@@ -116,6 +117,10 @@ void RenderTextControlSingleLine::layout()
         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);
@@ -164,6 +169,7 @@ void RenderTextControlSingleLine::layout()
     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.