diff -r 000000000000 -r 6474c204b198 content/base/src/nsViewportInfo.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/content/base/src/nsViewportInfo.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsViewportInfo.h"
+#include "mozilla/Assertions.h"
+#include <algorithm>
+
+using namespace mozilla;
+
+void
+nsViewportInfo::SetDefaultZoom(const CSSToScreenScale& aDefaultZoom)
+{
+  MOZ_ASSERT(aDefaultZoom.scale >= 0.0f);
+  mDefaultZoom = aDefaultZoom;
+}
+
+void
+nsViewportInfo::ConstrainViewportValues()
+{
+  // Constrain the min/max zoom as specified at:
+  // dev.w3.org/csswg/css-device-adapt section 6.2
+  mMaxZoom = std::max(mMinZoom, mMaxZoom);
+
+  mDefaultZoom = mDefaultZoom < mMaxZoom ? mDefaultZoom : mMaxZoom;
+  mDefaultZoom = mDefaultZoom > mMinZoom ? mDefaultZoom : mMinZoom;
+}