Update EXPORT_JSON to output stack samples in a matching format to the legacy viewer

R=ssid@google.com

Change-Id: I9efdad6b1a8a3d197898c63154787711bc8964ba

src/trace_processor/export_json_unittest.cc

diff --git a/src/trace_processor/export_json_unittest.cc b/src/trace_processor/export_json_unittest.cc
index c5c949a..6b7ad59 100644
--- a/src/trace_processor/export_json_unittest.cc
+++ b/src/trace_processor/export_json_unittest.cc
@@ -1189,7 +1189,8 @@
 
   EXPECT_EQ(result["traceEvents"].size(), 1u);
   Json::Value event = result["traceEvents"][0];
-  EXPECT_EQ(event["ph"].asString(), "I");
+  EXPECT_EQ(event["ph"].asString(), "n");
+  EXPECT_EQ(event["id"].asString(), "0x1");
   EXPECT_EQ(event["ts"].asInt64(), kTimestamp / 1000);
   EXPECT_EQ(event["tid"].asUInt(), kThreadID);
   EXPECT_EQ(event["cat"].asString(), "disabled_by_default-cpu_profiler");