Backed out changeset f713a828fe36 (bug 894931) since the backout it performed was already landed on mozilla-central (and wasn't identical)

layout/style/nsStyleStruct.cpp

@@ -2213,6 +2213,13 @@ nsStyleDisplay::nsStyleDisplay(const nsStyleDisplay& aSource)
   mPerspectiveOrigin[1] = aSource.mPerspectiveOrigin[1];
 }
 
+static uint8_t
+MapRelativePositionToStatic(uint8_t aPositionValue)
+{
+  return aPositionValue == NS_STYLE_POSITION_RELATIVE ?
+      NS_STYLE_POSITION_STATIC : aPositionValue;
+}
+
 nsChangeHint nsStyleDisplay::CalcDifference(const nsStyleDisplay& aOther) const
 {
   nsChangeHint hint = nsChangeHint(0);
@@ -2220,7 +2227,8 @@ nsChangeHint nsStyleDisplay::CalcDifference(const nsStyleDisplay& aOther) const
   // Changes between position:static and position:relative don't need
   // to reconstruct frames.
   if (!EqualURIs(mBinding, aOther.mBinding)
-      || mPosition != aOther.mPosition
+      || MapRelativePositionToStatic(mPosition) !=
+           MapRelativePositionToStatic(aOther.mPosition)
       || mDisplay != aOther.mDisplay
       || (mFloats == NS_STYLE_FLOAT_NONE) != (aOther.mFloats == NS_STYLE_FLOAT_NONE)
       || mOverflowX != aOther.mOverflowX
@@ -2229,6 +2237,11 @@ nsChangeHint nsStyleDisplay::CalcDifference(const nsStyleDisplay& aOther) const
     NS_UpdateHint(hint, nsChangeHint_ReconstructFrame);
   }
 
+  if (mPosition != aOther.mPosition) {
+    NS_UpdateHint(hint,
+      NS_CombineHint(nsChangeHint_NeedReflow, nsChangeHint_RepaintFrame));
+  }
+
   if (mFloats != aOther.mFloats) {
     // Changing which side we float on doesn't affect descendants directly
     NS_UpdateHint(hint,