wire up new json code in skiaserve

tools/debugger/SkDebugCanvas.cpp

Index: tools/debugger/SkDebugCanvas.cpp
diff --git a/tools/debugger/SkDebugCanvas.cpp b/tools/debugger/SkDebugCanvas.cpp
index d8d51fe0ace3b260bf360d27bd62f49cd9af0fb1..8b71c0fb2c44c55d9b7168b97585256372aa2dc9 100644
--- a/tools/debugger/SkDebugCanvas.cpp
+++ b/tools/debugger/SkDebugCanvas.cpp
@@ -318,11 +318,11 @@ SkTDArray <SkDrawCommand*>& SkDebugCanvas::getDrawCommands() {
     return fCommandVector;
 }
 
-Json::Value SkDebugCanvas::toJSON(UrlDataManager& urlDataManager) {
+Json::Value SkDebugCanvas::toJSON(UrlDataManager& urlDataManager, int n) {
     Json::Value result = Json::Value(Json::objectValue);
     result[SKDEBUGCANVAS_ATTRIBUTE_VERSION] = Json::Value(SKDEBUGCANVAS_VERSION);
     Json::Value commands = Json::Value(Json::arrayValue);
-    for (int i = 0; i < this->getSize(); i++) {
+    for (int i = 0; i < this->getSize() && i < n; i++) {
         commands[i] = this->getDrawCommandAt(i)->toJSON();
     }
     result[SKDEBUGCANVAS_ATTRIBUTE_COMMANDS] = commands;