Revert "SkShaderBase"

This reverts commit 58a756435ca3700d9766a4580bb0771a9774f603.

Reason for revert: g3, Android borkage.

Original change's description:
> SkShaderBase
> 
> Introduce a private base class (SkShaderBase), to hide
> implementation details from the public interface (SkShader).
> 
> Change-Id: If3ec26ca6abc9da20e3f139c11fdc023bdd85176
> Reviewed-on: https://skia-review.googlesource.com/17241
> Commit-Queue: Florin Malita <fmalita@chromium.org>
> Reviewed-by: Mike Reed <reed@google.com>
> 

TBR=mtklein@google.com,fmalita@chromium.org,reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I32b012ee466dd006c074593f211f43ed602f1078
Reviewed-on: https://skia-review.googlesource.com/17845
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/src/effects/gradients/Sk4fGradientBase.h b/src/effects/gradients/Sk4fGradientBase.h
index a660d6b..9209a90 100644
--- a/src/effects/gradients/Sk4fGradientBase.h
+++ b/src/effects/gradients/Sk4fGradientBase.h
@@ -14,7 +14,7 @@
 #include "SkMatrix.h"
 #include "SkNx.h"
 #include "SkPM4f.h"
-#include "SkShaderBase.h"
+#include "SkShader.h"
 #include "SkTArray.h"
 
 struct Sk4fGradientInterval {
@@ -53,7 +53,7 @@
 };
 
 class SkGradientShaderBase::
-GradientShaderBase4fContext : public Context {
+GradientShaderBase4fContext : public SkShader::Context {
 public:
     GradientShaderBase4fContext(const SkGradientShaderBase&,
                                 const ContextRec&);
@@ -77,7 +77,7 @@
     bool                       fColorsArePremul;
 
 private:
-    using INHERITED = Context;
+    using INHERITED = SkShader::Context;
 
     void addMirrorIntervals(const SkGradientShaderBase&,
                             const Sk4f& componentScale, bool reverse);