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/bench/SkLinearBitmapPipelineBench.cpp b/bench/SkLinearBitmapPipelineBench.cpp
index bbacac7..0a86778 100644
--- a/bench/SkLinearBitmapPipelineBench.cpp
+++ b/bench/SkLinearBitmapPipelineBench.cpp
@@ -15,7 +15,7 @@
 #include "SkImage.h"
 #include "SkLinearBitmapPipeline.h"
 #include "SkPM4f.h"
-#include "SkShaderBase.h"
+#include "SkShader.h"
 
 struct CommonBitmapFPBenchmark : public Benchmark {
     CommonBitmapFPBenchmark(
@@ -201,10 +201,10 @@
         SkAutoTMalloc<SkPMColor> buffer4b(width*height);
 
         SkArenaAlloc alloc{0};
-        const SkShaderBase::ContextRec rec(fPaint, fM, nullptr,
-                                           SkShaderBase::ContextRec::kPMColor_DstType,
-                                           nullptr);
-        SkShaderBase::Context* ctx = as_SB(fPaint.getShader())->makeContext(rec, &alloc);
+        const SkShader::ContextRec rec(fPaint, fM, nullptr,
+                                       SkShader::ContextRec::kPMColor_DstType,
+                                       nullptr);
+        SkShader::Context* ctx = fPaint.getShader()->makeContext(rec, &alloc);
 
         int count = 100;