Clean up test drawContext usage

tools/debugger/SkDebugCanvas.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvasPriv.h"
 #include "SkClipStack.h"
 #include "SkDebugCanvas.h"
@@ skipping 400 matching lines @@
     return fCommandVector;
 }
 
 SkTDArray <SkDrawCommand*>& SkDebugCanvas::getDrawCommands() {
     return fCommandVector;
 }
 
 GrAuditTrail* SkDebugCanvas::getAuditTrail(SkCanvas* canvas) {
     GrAuditTrail* at = nullptr;
 #if SK_SUPPORT_GPU
-    GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
-    if (rt) {
-        GrContext* ctx = rt->getContext();
-        if (ctx) {
-            at = ctx->getAuditTrail();
-        }
+    GrContext* ctx = canvas->getGrContext();
+    if (ctx) {
+        at = ctx->getAuditTrail();
     }
 #endif
     return at;
 }
 
 void SkDebugCanvas::drawAndCollectBatches(int n, SkCanvas* canvas) {
 #if SK_SUPPORT_GPU
     GrAuditTrail* at = this->getAuditTrail(canvas);
     if (at) {
         // loop over all of the commands and draw them, this is to collect reordering
@@ skipping 369 matching lines @@
 }
 
 bool SkDebugCanvas::lastClipStackData(const SkPath& devPath) {
     if (fCalledAddStackData) {
         fClipStackData.appendf("<br>");
         addPathData(devPath, "pathOut");
         return true;
     }
     return false;
 }