Revert of Don't always repaint on zIndex change

Revert of Don't always repaint on zIndex change (https://codereview.chromium.org/240253007/)

Reason for revert:
Depends on https://codereview.chromium.org/203463007/ which broke ChromeOS login window: https://code.google.com/p/chromium/issues/detail?id=365507

Original issue's description:
> Don't always repaint on zIndex change
> 
> If zIndex of a composited layer changes and there is no other conditions
> triggering repaint, we should not repaint the layer.
> 
> Now treat zIndex change like opacity change about repainting.
> 
> BUG=364636
> TEST=reuse existing compositing/repaint/should-not-repaint-composited-descendants.html
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=171989

TBR=esprehn@chromium.org,eseidel@chromium.org,ojan@chromium.org,wangxianzhu@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=364636
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172172

[aboxhall, 2014-04-22 20:14:09]

Created Revert of Don't always repaint on zIndex change

[commit-bot: I haz the power, 2014-04-22 20:14:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/aboxhall@chromium.org/247293006/1

[commit-bot: I haz the power, 2014-04-22 20:14:58]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-22 20:14:58]

Failed to apply patch for Source/core/rendering/style/RenderStyle.cpp:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file Source/core/rendering/style/RenderStyle.cpp
  Hunk #1 FAILED at 605.
  1 out of 1 hunk FAILED -- saving rejects to file
Source/core/rendering/style/RenderStyle.cpp.rej

Patch:       Source/core/rendering/style/RenderStyle.cpp
Index: Source/core/rendering/style/RenderStyle.cpp
diff --git a/Source/core/rendering/style/RenderStyle.cpp
b/Source/core/rendering/style/RenderStyle.cpp
index
634cb8a2630430a34db7e24667a72f412afe5aed..ef055cc18964eb27de23fcfc35cacc2efc0dc50e
100644
--- a/Source/core/rendering/style/RenderStyle.cpp
+++ b/Source/core/rendering/style/RenderStyle.cpp
@@ -605,14 +605,9 @@
 
 StyleDifferenceLegacy RenderStyle::repaintOnlyDiff(const RenderStyle& other,
unsigned& changedContextSensitiveProperties) const
 {
-    // FIXME: The condition for zIndex may be incorrect or unnecessary.
-    // See StyleAdjuster::adjustRenderStyle() for the conditions that zIndex is
applicable.
-    if (position() != StaticPosition) {
-        if (m_box->zIndex() != other.m_box->zIndex() || m_box->hasAutoZIndex()
!= other.m_box->hasAutoZIndex())
-            changedContextSensitiveProperties |=
ContextSensitivePropertyZIndex;
-        if (visual->clip != other.visual->clip || visual->hasClip !=
other.visual->hasClip)
-            return StyleDifferenceRepaintLayer;
-    }
+    if (position() != StaticPosition && (m_box->zIndex() !=
other.m_box->zIndex() || m_box->hasAutoZIndex() != other.m_box->hasAutoZIndex()
+        || visual->clip != other.visual->clip || visual->hasClip !=
other.visual->hasClip))
+        return StyleDifferenceRepaintLayer;
 
     if (RuntimeEnabledFeatures::cssCompositingEnabled() &&
(rareNonInheritedData->m_effectiveBlendMode !=
other.rareNonInheritedData->m_effectiveBlendMode
         || rareNonInheritedData->m_isolation !=
other.rareNonInheritedData->m_isolation))

[aboxhall, 2014-04-22 20:55:14]

The CQ bit was checked by aboxhall@chromium.org

[commit-bot: I haz the power, 2014-04-22 20:55:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/aboxhall@chromium.org/247293006/120001

[commit-bot: I haz the power, 2014-04-22 20:56:06]

Change committed as 172172