Extend composeshader to support a lerp parameter

Bug: skia:
Change-Id: I3bbb2cb8d0a84fca0309654498548ebc94d8938f
Reviewed-on: https://skia-review.googlesource.com/18460
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
diff --git a/src/core/SkDraw_vertices.cpp b/src/core/SkDraw_vertices.cpp
index d0ef2d7..4f7fc13 100644
--- a/src/core/SkDraw_vertices.cpp
+++ b/src/core/SkDraw_vertices.cpp
@@ -247,7 +247,7 @@
             matrix43 = triShader->getMatrix43();
             if (shader) {
                 shader = outerAlloc.make<SkComposeShader>(sk_ref_sp(triShader), sk_ref_sp(shader),
-                                                          bmode);
+                                                          bmode, 1);
             } else {
                 shader = triShader;
             }