Add abilitly to query audit trail for batches by draw op

tools/skiaserve/Request.cpp

Index: tools/skiaserve/Request.cpp
diff --git a/tools/skiaserve/Request.cpp b/tools/skiaserve/Request.cpp
index 4d256d56d87260af82172ad0cdeb87a408f9f278..bcaebde01f518e756c4da1a1f0be480601e4e047 100644
--- a/tools/skiaserve/Request.cpp
+++ b/tools/skiaserve/Request.cpp
@@ -138,6 +138,28 @@ bool Request::enableGPU(bool enable) {
     return true;
 }
 
+GrAuditTrail* Request::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();
+        }
+    }
+#endif
+    return at;
+}
+
+void Request::cleanupAuditTrail(SkCanvas* canvas) {
+    GrAuditTrail* at = this->getAuditTrail(canvas);
+    if (at) {
+        GrAuditTrail::AutoEnable ae(at);
+        at->fullReset();
+    }
+}
+
 SkData* Request::getJsonOps(int n) {
     SkCanvas* canvas = this->getCanvas();
     Json::Value root = fDebugCanvas->toJSON(fUrlDataManager, n, canvas);
@@ -145,6 +167,8 @@ SkData* Request::getJsonOps(int n) {
     SkDynamicMemoryWStream stream;
     stream.writeText(Json::FastWriter().write(root).c_str());
 
+    this->cleanupAuditTrail(canvas);
+
     return stream.copyToData();
 }
 
@@ -156,11 +180,7 @@ SkData* Request::getJsonBatchList(int n) {
     // a Json::Value and is only compiled in this file
     Json::Value parsedFromString;
 #if SK_SUPPORT_GPU
-    GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
-    SkASSERT(rt);
-    GrContext* ctx = rt->getContext();
-    SkASSERT(ctx);
-    GrAuditTrail* at = ctx->getAuditTrail();
+    GrAuditTrail* at = this->getAuditTrail(canvas);
     GrAuditTrail::AutoManageBatchList enable(at);
     
     fDebugCanvas->drawTo(canvas, n);