Bug 665597 - Use saturating calculations when adding the margin to the scrollable overflow rect. part=4/5 r=roc

gfx/src/nsRect.h

@@ -81,6 +81,44 @@ struct NS_GFX nsRect :
   }
 #endif
 
+  // A version of Inflate that caps the values to the nscoord range.
+  // x & y is capped at the minimum value nscoord_MIN and
+  // width & height is capped at the maximum value nscoord_MAX.
+  void SaturatingInflate(const nsMargin& aMargin)
+  {
+#ifdef NS_COORD_IS_FLOAT
+    Inflate(aMargin);
+#else
+    PRInt64 nx = PRInt64(x) - aMargin.left;
+    if (nx < nscoord_MIN) {
+      NS_WARNING("Underflowed nscoord_MIN in conversion to nscoord x");
+      nx = nscoord_MIN;
+    }
+    x = nscoord(nx);
+
+    PRInt64 ny = PRInt64(y) - aMargin.top;
+    if (ny < nscoord_MIN) {
+      NS_WARNING("Underflowed nscoord_MIN in conversion to nscoord y");
+      ny = nscoord_MIN;
+    }
+    y = nscoord(ny);
+
+    PRInt64 w = PRInt64(width) + PRInt64(aMargin.left) + aMargin.right;
+    if (w > nscoord_MAX) {
+      NS_WARNING("Overflowed nscoord_MAX in conversion to nscoord width");
+      w = nscoord_MAX;
+    }
+    width = nscoord(w);
+
+    PRInt64 h = PRInt64(height) + PRInt64(aMargin.top) + aMargin.bottom;
+    if (h > nscoord_MAX) {
+      NS_WARNING("Overflowed nscoord_MAX in conversion to nscoord height");
+      h = nscoord_MAX;
+    }
+    height = nscoord(h);
+#endif
+  }
+
   // We have saturating versions of all the Union methods. These avoid
   // overflowing nscoord values in the 'width' and 'height' fields by
   // clamping the width and height values to nscoord_MAX if necessary.

layout/generic/nsFrame.cpp

@@ -6605,9 +6605,9 @@ nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
       nsRect marginBounds(bounds);
       nsMargin margin = GetUsedMargin();
       ApplySkipSides(margin);
-      marginBounds.Inflate(margin);
+      marginBounds.SaturatingInflate(margin);
       nsRect& so = aOverflowAreas.ScrollableOverflow();
-      so.UnionRectEdges(so, marginBounds);
+      so.SaturatingUnionRectEdges(so, marginBounds);
     }
   }