perfetto: Remove unexpected closing brace in JSONTraceExporter.

Might have snuck in during the refactor :)

Change-Id: Iacb0743719deae0c998066226db4198492c15ecc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1505634Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Auto-Submit: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638118}

services/tracing/perfetto/json_trace_exporter.cc

@@ -36,6 +36,8 @@ void JSONTraceExporter::OnTraceData(std::vector<perfetto::TracePacket> packets,
                                     bool has_more) {
   DCHECK(!packets.empty() || !has_more);
 
+  // TODO(eseckler): |label_filter_| seems broken for anything but
+  // "traceEvents" (e.g. "systemTraceEvents" will output invalid JSON).
   if (label_filter_.empty() && !has_output_json_preamble_) {
     out_ += "{\"traceEvents\":[";
     has_output_json_preamble_ = true;
@@ -77,10 +79,10 @@ void JSONTraceExporter::OnTraceData(std::vector<perfetto::TracePacket> packets,
         base::JSONWriter::Write(*metadata_, &json_value);
         out_ += json_value;
       }
-    }
 
-    // Finish the json object we started in the preamble.
-    out_ += "}";
+      // Finish the json object we started in the preamble.
+      out_ += "}";
+    }
   }
 
   // Send any remaining data. There is no harm issuing the callback with an