From daea81cf90105dd73c1cdd9bfe1a806eb7dc8a18 Mon Sep 17 00:00:00 2001
From: Matt Woodrow <mwoodrow@mozilla.com>
Date: Thu, 7 Apr 2016 18:51:45 +1200
Subject: [PATCH] Bug 1251644 - Snap object-contain fit if we were going to
 reduce the size by less than one css pixel. r=seth

---
 layout/base/nsCSSRendering.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/layout/base/nsCSSRendering.cpp b/layout/base/nsCSSRendering.cpp
index 1ee3978715ab..2642373c4d3b 100644
--- a/layout/base/nsCSSRendering.cpp
+++ b/layout/base/nsCSSRendering.cpp
@@ -4990,9 +4990,17 @@ nsImageRenderer::ComputeConstrainedSize(const nsSize& aConstrainingSize,
     size.width = aConstrainingSize.width;
     size.height = NSCoordSaturatingNonnegativeMultiply(
                     aIntrinsicRatio.height, scaleX);
+    // If we're reducing the size by less than one css pixel, then just use the
+    // constraining size.
+    if (aFitType == CONTAIN && aConstrainingSize.height - size.height < nsPresContext::AppUnitsPerCSSPixel()) {
+      size.height = aConstrainingSize.height;
+    }
   } else {
     size.width = NSCoordSaturatingNonnegativeMultiply(
                    aIntrinsicRatio.width, scaleY);
+    if (aFitType == CONTAIN && aConstrainingSize.width - size.width < nsPresContext::AppUnitsPerCSSPixel()) {
+      size.width = aConstrainingSize.width;
+    }
     size.height = aConstrainingSize.height;
   }
   return size;