Update gtest/gmock to use system includes

Change-Id: I3ba2be768451e417ef273c933a6bf89f3f93a2e6
diff --git a/src/trace_processor/export_json_unittest.cc b/src/trace_processor/export_json_unittest.cc
index 2f6dde5..c9c82a9 100644
--- a/src/trace_processor/export_json_unittest.cc
+++ b/src/trace_processor/export_json_unittest.cc
@@ -18,8 +18,8 @@
 
 #include "perfetto/base/temp_file.h"
 
-#include "gmock/gmock.h"
-#include "gtest/gtest.h"
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
 
 #include <json/reader.h>
 #include <json/value.h>