add localMatrix to gradient Descriptor

this consolidation will also help transisition to new flattening pattern, where we want to
have a flatten/unflatten method on all of the common gradient params (i.e. Descriptor).

BUG=skia:
R=egdaniel@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/461643002
diff --git a/src/effects/gradients/SkTwoPointRadialGradient.cpp b/src/effects/gradients/SkTwoPointRadialGradient.cpp
index 16b4da5..8a40822 100644
--- a/src/effects/gradients/SkTwoPointRadialGradient.cpp
+++ b/src/effects/gradients/SkTwoPointRadialGradient.cpp
@@ -167,15 +167,15 @@
 
 /////////////////////////////////////////////////////////////////////
 
-SkTwoPointRadialGradient::SkTwoPointRadialGradient(
-    const SkPoint& start, SkScalar startRadius,
-    const SkPoint& end, SkScalar endRadius,
-    const Descriptor& desc, const SkMatrix* localMatrix)
-    : SkGradientShaderBase(desc, localMatrix),
-      fCenter1(start),
-      fCenter2(end),
-      fRadius1(startRadius),
-      fRadius2(endRadius) {
+SkTwoPointRadialGradient::SkTwoPointRadialGradient(const SkPoint& start, SkScalar startRadius,
+                                                   const SkPoint& end, SkScalar endRadius,
+                                                   const Descriptor& desc)
+    : SkGradientShaderBase(desc)
+    , fCenter1(start)
+    , fCenter2(end)
+    , fRadius1(startRadius)
+    , fRadius2(endRadius)
+{
     init();
 }