Fix some bugs and performance issues with skiaserve

src/gpu/GrAuditTrail.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrAuditTrail.h"
 #include "batches/GrBatch.h"
 
@@ skipping 129 matching lines @@
 }
 
 template <typename T>
 void GrAuditTrail::JsonifyTArray(SkString* json, const char* name, const T& array,
                                  bool addComma) {
     if (array.count()) {
         if (addComma) {
             json->appendf(",");
         }
         json->appendf("\"%s\": [", name);
+        const char* separator = "";
         for (int i = 0; i < array.count(); i++) {
             // Handle sentinel nullptrs
-            if (!array[i]) {
-                continue;
-            }
-            json->append(array[i]->toJson());
-            if (i < array.count() - 1) {
-                json->append(",");
+            if (array[i]) {
+                json->appendf("%s", separator);
+                json->append(array[i]->toJson());
+                separator = ",";
             }
         }
         json->append("]");
     }
 }
 
 // This will pretty print a very small subset of json
 // The parsing rules are straightforward, aside from the fact that we do not want an extra newline
 // before ',' and after '}', so we have a comma exception rule.
 class PrettyPrintJson {
@@ skipping 122 matching lines @@
 
 SkString GrAuditTrail::BatchNode::toJson() const {
     SkString json;
     json.append("{");
     json.appendf("\"RenderTarget\": \"%u\",", fRenderTargetUniqueID);
     skrect_to_json(&json, "Bounds", fBounds);
     JsonifyTArray(&json, "Batches", fChildren, true);
     json.append("}");
     return json;
 }