Delete GradientShaderCache

Dead code.

Change-Id: If415e603b8e898da72ad95f32596445900794d23
Reviewed-on: https://skia-review.googlesource.com/63562
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/src/shaders/gradients/SkRadialGradient.cpp b/src/shaders/gradients/SkRadialGradient.cpp
index d411c3a..5014eae 100644
--- a/src/shaders/gradients/SkRadialGradient.cpp
+++ b/src/shaders/gradients/SkRadialGradient.cpp
@@ -7,6 +7,9 @@
 
 #include "SkColorSpaceXformer.h"
 #include "SkRadialGradient.h"
+#include "SkRasterPipeline.h"
+#include "SkReadBuffer.h"
+#include "SkWriteBuffer.h"
 
 namespace {