diff -r 000000000000 -r 6474c204b198 gfx/2d/unittest/TestCairo.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/2d/unittest/TestCairo.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,53 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "cairo.h"
+
+#include "gtest/gtest.h"
+
+namespace mozilla {
+namespace layers {
+
+void TryCircle(double centerX, double centerY, double radius) {
+  printf("TestCairo:TryArcs centerY %f, radius %f\n",centerY,radius);
+
+  cairo_surface_t *surf = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,8,21);
+  ASSERT_TRUE(surf != nullptr);
+
+  cairo_t *cairo = cairo_create(surf);
+  ASSERT_TRUE(cairo != nullptr);
+
+  cairo_set_antialias(cairo, CAIRO_ANTIALIAS_NONE);
+  cairo_arc(cairo, 0.0, centerY, radius, 0.0, 6.2831853071795862);
+  cairo_fill_preserve(cairo);
+
+  cairo_surface_destroy(surf);
+  cairo_destroy(cairo);
+}
+
+TEST(Cairo, Simple) {
+  TryCircle(0.0, 0.0, 14.0);
+  TryCircle(0.0, 1.0, 22.4);
+  TryCircle(1.0, 0.0, 1422.4);
+  TryCircle(1.0, 1.0, 3422.4);
+  TryCircle(-10.0, 1.0, -2);
+}
+
+TEST(Cairo, Bug825721) {
+  // OK:
+  TryCircle(0.0, 0.0, 8761126469220696064.0);
+  TryCircle(0.0, 1.0, 8761126469220696064.0);
+
+  // OK:
+  TryCircle(1.0, 0.0, 5761126469220696064.0);
+
+  // This was the crash in 825721.  Note that centerY has to be non-zero,
+  // and radius has to be not only large, but in particular range.
+  // 825721 has a band-aid fix, where the crash is inevitable, but does
+  // not fix the cause.  The same code crashes in cairo standalone.
+  TryCircle(0.0, 1.0, 5761126469220696064.0);
+}
+
+}
+}