Clean up test drawContext usage

tools/debugger/SkDebugCanvas.cpp

Index: tools/debugger/SkDebugCanvas.cpp
diff --git a/tools/debugger/SkDebugCanvas.cpp b/tools/debugger/SkDebugCanvas.cpp
index 8568029d38e970257c599052577703d703a6e600..5ee22eba3fe9e83f00d038371af018067b8960be 100644
--- a/tools/debugger/SkDebugCanvas.cpp
+++ b/tools/debugger/SkDebugCanvas.cpp
@@ -418,12 +418,9 @@ SkTDArray <SkDrawCommand*>& SkDebugCanvas::getDrawCommands() {
 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;