Move most of the transform logic into the primitive processors

BUG=skia:

Review URL: https://codereview.chromium.org/822423004
diff --git a/include/gpu/GrFragmentProcessor.h b/include/gpu/GrFragmentProcessor.h
index fe6e6fa..341b3fb 100644
--- a/include/gpu/GrFragmentProcessor.h
+++ b/include/gpu/GrFragmentProcessor.h
@@ -47,6 +47,10 @@
         numTransforms(). */
     const GrCoordTransform& coordTransform(int index) const { return *fCoordTransforms[index]; }
 
+    const SkTArray<const GrCoordTransform*, true>& coordTransforms() const {
+        return fCoordTransforms;
+    }
+
     /** Will this prceossor read the destination pixel value? */
     bool willReadDstColor() const { return fWillReadDstColor; }