Added check for ill-conditioned invert

include/core/SkScalar.h

Index: include/core/SkScalar.h
diff --git a/include/core/SkScalar.h b/include/core/SkScalar.h
index 2c42eb8e895b371fad9713a0af0e57f3e74f87de..f27c56e331d0c8b90c38bbcca9b1c254f8c87de1 100644
--- a/include/core/SkScalar.h
+++ b/include/core/SkScalar.h
@@ -28,6 +28,7 @@ typedef float SkScalar;
 #define SK_ScalarTanPIOver8         0.414213562f
 #define SK_ScalarRoot2Over2         0.707106781f
 #define SK_ScalarMax                3.402823466e+38f
+#define SK_ScalarSmallest           1.17549435e-38f
 #define SK_ScalarInfinity           SK_FloatInfinity
 #define SK_ScalarNegativeInfinity   SK_FloatNegativeInfinity
 #define SK_ScalarNaN                SK_FloatNaN
@@ -71,6 +72,7 @@ typedef double SkScalar;
 #define SK_ScalarTanPIOver8         0.4142135623731
 #define SK_ScalarRoot2Over2         0.70710678118655
 #define SK_ScalarMax                1.7976931348623157+308
+#define SK_ScalarSmallest           2.2250738585072014e-308
 #define SK_ScalarInfinity           SK_DoubleInfinity
 #define SK_ScalarNegativeInfinity   SK_DoubleNegativeInfinity
 #define SK_ScalarNaN                SK_DoubleNaN