diff -r 000000000000 -r 6474c204b198 gfx/skia/trunk/src/utils/SkCubicInterval.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/skia/trunk/src/utils/SkCubicInterval.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,67 @@
+
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "SkCubicInterval.h"
+
+static SkScalar eval_cubic(SkScalar c1, SkScalar c2, SkScalar c3,
+                           SkScalar t) {
+    return SkScalarMul(SkScalarMul(SkScalarMul(c3, t) + c2, t) + c1, t);
+}
+
+static SkScalar find_cubic_t(SkScalar c1, SkScalar c2, SkScalar c3,
+                             SkScalar targetX) {
+    SkScalar minT = 0;
+    SkScalar maxT = SK_Scalar1;
+    SkScalar t;
+
+    for (;;) {
+        t = SkScalarAve(minT, maxT);
+        SkScalar x = eval_cubic(c1, c2, c3, t);
+        if (SkScalarNearlyZero(x - targetX)) {
+            break;
+        }
+        // subdivide the range and try again
+        if (x < targetX) {
+            minT = t;
+        } else {
+            maxT = t;
+        }
+    }
+    return t;
+}
+
+/*
+    a(1-t)^3 + 3bt(1-t)^2 + 3ct^2(1-t) + dt^3
+    a: [0, 0]
+    d: [1, 1]
+
+    3bt - 6bt^2 + 3bt^3 + 3ct^2 - 3ct^3 + t^3
+    C1 = t^1: 3b
+    C2 = t^2: 3c - 6b
+    C3 = t^3: 3b - 3c + 1
+
+    ((C3*t + C2)*t + C1)*t
+ */
+SkScalar SkEvalCubicInterval(SkScalar x1, SkScalar y1,
+                             SkScalar x2, SkScalar y2,
+                             SkScalar unitX) {
+    x1 = SkScalarPin(x1, 0, SK_Scalar1);
+    x2 = SkScalarPin(x2, 0, SK_Scalar1);
+    unitX = SkScalarPin(unitX, 0, SK_Scalar1);
+
+    // First compute our coefficients in X
+    x1 *= 3;
+    x2 *= 3;
+
+    // now search for t given unitX
+    SkScalar t = find_cubic_t(x1, x2 - 2*x1, x1 - x2 + SK_Scalar1, unitX);
+
+    // now evaluate the cubic in Y
+    y1 *= 3;
+    y2 *= 3;
+    return eval_cubic(y1, y2 - 2*y1, y1 - y2 + SK_Scalar1, t);
+}