Fix size of rotated text with FreeType.

src/utils/SkMatrix22.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkPoint.h"
+
+class SkMatrix;
+
+/** Find the Givens matrix G, which is the rotational matrix
+ *  that rotates the vector h to the positive hoizontal axis.
+ *  G * h = [hypot(h), 0]
+ *
+ *  This is equivalent to
+ *
+ *  SkScalar r = h.length();
+ *  SkScalar r_inv = r ? SkScalarInvert(r) : 0;
+ *  h.scale(r_inv);
+ *  G->setSinCos(-h.fY, h.fX);
+ *
+ *  but has better numerical stability by using (partial) hypot,
+ *  and saves a multiply by not computing r.
+ */
+void SkComputeGivensRotation(const SkVector& h, SkMatrix* G);