use Descriptor struct to encapsulate all the common paramaeters between our various gradient types. If we like it, might promote it to the public API.

BUG=
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/15733007

git-svn-id: http://skia.googlecode.com/svn/trunk@9260 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/gradients/SkLinearGradient.cpp b/src/effects/gradients/SkLinearGradient.cpp
index e0f216c..4bc697d 100644
--- a/src/effects/gradients/SkLinearGradient.cpp
+++ b/src/effects/gradients/SkLinearGradient.cpp
@@ -62,13 +62,8 @@
 
 ///////////////////////////////////////////////////////////////////////////////
 
-SkLinearGradient::SkLinearGradient(const SkPoint pts[2],
-                                   const SkColor colors[],
-                                   const SkScalar pos[],
-                                   int colorCount,
-                                   SkShader::TileMode mode,
-                                   SkUnitMapper* mapper)
-    : SkGradientShaderBase(colors, pos, colorCount, mode, mapper)
+SkLinearGradient::SkLinearGradient(const SkPoint pts[2], const Descriptor& desc)
+    : SkGradientShaderBase(desc)
     , fStart(pts[0])
     , fEnd(pts[1]) {
     pts_to_unit_matrix(pts, &fPtsToUnit);