Don't force full invalidation on padding or margin change

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 43fedd29bc3bc2361fad3db8cb6022937664b6d5..3862be58f61ec13e57923a7ba47e39b18bb7ff28 100644
--- a/Source/core/rendering/style/RenderStyle.cpp
+++ b/Source/core/rendering/style/RenderStyle.cpp
@@ -423,12 +423,6 @@ bool RenderStyle::diffNeedsFullLayoutAndRepaint(const RenderStyle& other) const
     //   instead of forced full repaint.
 
     if (surround.get() != other.surround.get()) {

[Julien - ping for review, 2014/06/29 01:20:32]

There is only border checks in this branch so I would just remove this check.

[Xianzhu, 2014/06/30 22:30:34]

If 'surround' object is shared between the old style and the new style, the
above check will save 2 to 8 border width getters (which contain logic) and 1 to
4 border width comparisons.

-        if (surround->margin != other.surround->margin)
-            return true;
-
-        if (surround->padding != other.surround->padding)
-            return true;
-
         // If our border widths change, then we need to layout. Other changes to borders only necessitate a repaint.
         if (borderLeftWidth() != other.borderLeftWidth()
             || borderTopWidth() != other.borderTopWidth()
@@ -616,6 +610,14 @@ bool RenderStyle::diffNeedsFullLayout(const RenderStyle& other) const
     if (noninherited_flags._vertical_align != other.noninherited_flags._vertical_align)
         return true;
 
+    if (surround.get() != other.surround.get()) {

[Julien - ping for review, 2014/06/29 01:20:32]

Will this work correctly if we have a background-clip: padding-box (or anything
bigger) and we resize the box without changing the overall size (by shrinking
the padding but increasing border so that the content box and border box are the
same)?

[Xianzhu, 2014/06/30 22:30:34]

Yes. Border size change will still trigger a full repaint.

Added a test case.

+        if (surround->margin != other.surround->margin)
+            return true;
+
+        if (surround->padding != other.surround->padding)
+            return true;
+    }
+
     return false;
 }