diff -r 000000000000 -r 6474c204b198 mobile/android/base/gfx/DisplayPortMetrics.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/gfx/DisplayPortMetrics.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,78 @@
+/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
+ * 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/. */
+
+package org.mozilla.gecko.gfx;
+
+import org.mozilla.gecko.mozglue.generatorannotations.WrapElementForJNI;
+import org.mozilla.gecko.util.FloatUtils;
+
+import android.graphics.RectF;
+
+/*
+ * This class keeps track of the area we request Gecko to paint, as well
+ * as the resolution of the paint. The area may be different from the visible
+ * area of the page, and the resolution may be different from the resolution
+ * used in the compositor to render the page. This is so that we can ask Gecko
+ * to paint a much larger area without using extra memory, and then render some
+ * subsection of that with compositor scaling.
+ */
+public final class DisplayPortMetrics {
+    @WrapElementForJNI
+    public final float resolution;
+    @WrapElementForJNI
+    private final RectF mPosition;
+
+    public DisplayPortMetrics() {
+        this(0, 0, 0, 0, 1);
+    }
+
+    @WrapElementForJNI
+    public DisplayPortMetrics(float left, float top, float right, float bottom, float resolution) {
+        this.resolution = resolution;
+        mPosition = new RectF(left, top, right, bottom);
+    }
+
+    public float getLeft() {
+        return mPosition.left;
+    }
+
+    public float getTop() {
+        return mPosition.top;
+    }
+
+    public float getRight() {
+        return mPosition.right;
+    }
+
+    public float getBottom() {
+        return mPosition.bottom;
+    }
+
+    public boolean contains(RectF rect) {
+        return mPosition.contains(rect);
+    }
+
+    public boolean fuzzyEquals(DisplayPortMetrics metrics) {
+        return RectUtils.fuzzyEquals(mPosition, metrics.mPosition)
+            && FloatUtils.fuzzyEquals(resolution, metrics.resolution);
+    }
+
+    public String toJSON() {
+        StringBuilder sb = new StringBuilder(256);
+        sb.append("{ \"left\": ").append(mPosition.left)
+          .append(", \"top\": ").append(mPosition.top)
+          .append(", \"right\": ").append(mPosition.right)
+          .append(", \"bottom\": ").append(mPosition.bottom)
+          .append(", \"resolution\": ").append(resolution)
+          .append('}');
+        return sb.toString();
+    }
+
+    @Override
+    public String toString() {
+        return "DisplayPortMetrics v=(" + mPosition.left + "," + mPosition.top + "," + mPosition.right + ","
+                + mPosition.bottom + ") z=" + resolution;
+    }
+}