Make SkMatrix::get*Scale[s]() fail on NaN

include/core/SkMatrix.h

Index: include/core/SkMatrix.h
diff --git a/include/core/SkMatrix.h b/include/core/SkMatrix.h
index 97a53505ef3734ae36de8d5e0799b07d4c4e075a..0a0f3cf96ac61ffedcbbb92e554257151d1ca71f 100644
--- a/include/core/SkMatrix.h
+++ b/include/core/SkMatrix.h
@@ -635,15 +635,17 @@ public:
 
     /**
      * Calculates the minimum scaling factor of the matrix as computed from the SVD of the upper
-     * left 2x2. If the matrix has perspective -1 is returned.
+     * left 2x2. If the max scale factor cannot be computed (for example overflow or perspective)
+     * -1 is returned.
      *
-     * @return minumum scale factor
+     * @return minimum scale factor
      */
     SkScalar getMinScale() const;
 
     /**
      * Calculates the maximum scaling factor of the matrix as computed from the SVD of the upper
-     * left 2x2. If the matrix has perspective -1 is returned.
+     * left 2x2. If the max scale factor cannot be computed (for example overflow or perspective)
+     * -1 is returned.
      *
      * @return maximum scale factor
      */
@@ -651,8 +653,8 @@ public:
 
     /**
      * Gets both the min and max scale factors. The min scale factor is scaleFactors[0] and the max
-     * is scaleFactors[1]. If the matrix has perspective false will be returned and scaleFactors
-     * will be unchanged.
+     * is scaleFactors[1]. If the min/max scale factors cannot be computed false is returned and the
+     * values of scaleFactors[] are undefined.

[reed1, 2015/12/17 21:04:26]

consider adding SK_WARN_UNUSED_RESULT ?

      */
     bool getMinMaxScales(SkScalar scaleFactors[2]) const;