Revise SVD code to remove arctangents.

src/core/SkMatrixUtils.h

Index: src/core/SkMatrixUtils.h
diff --git a/src/core/SkMatrixUtils.h b/src/core/SkMatrixUtils.h
index 37341f289e5bba4d73d695016d4839d497448069..3fc1440e15ea7a7683f0a1cbd8390b083e9bbcfb 100644
--- a/src/core/SkMatrixUtils.h
+++ b/src/core/SkMatrixUtils.h
@@ -40,15 +40,15 @@ static inline bool SkTreatAsSpriteFilter(const SkMatrix& matrix,
     return SkTreatAsSprite(matrix, width, height, kSkSubPixelBitsForBilerp);
 }
 
-/** Decomposes the upper-left 2x2 of the matrix into a rotation, followed by a non-uniform scale,
-    followed by another rotation. Returns true if successful.
-    If the scale factors are uniform, then rotation1 will be 0.
-    If there is a reflection, yScale will be negative.
-    Returns false if the matrix is degenerate.
+/** Decomposes the upper-left 2x2 of the matrix into a rotation (represented by
+    the cosine and sine of the rotation angle), followed by a non-uniform scale,
+    followed by another rotation. If there is a reflection, one of the scale 
+    factors will be negative.
+    Returns true if successful. Returns false if the matrix is degenerate.
     */
 bool SkDecomposeUpper2x2(const SkMatrix& matrix,
-                         SkScalar* rotation0,
-                         SkScalar* xScale, SkScalar* yScale,
-                         SkScalar* rotation1);
+                         SkPoint* rotation1,
+                         SkPoint* scale,
+                         SkPoint* rotation2);
 
 #endif