telemetry_AFDOGenerate: Add --legacy-json-trace-format flag.

BUG=chromium:1045159
TEST=Tested option by hand and it worked.

Change-Id: Iacc6f52d7c37572f62694a70d4315f6a147546d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2018126
Reviewed-by: Luis Lozano <llozano@chromium.org>
Commit-Queue: Caroline Tice <cmtice@chromium.org>
Tested-by: Caroline Tice <cmtice@chromium.org>
diff --git a/server/site_tests/telemetry_AFDOGenerate/telemetry_AFDOGenerate.py b/server/site_tests/telemetry_AFDOGenerate/telemetry_AFDOGenerate.py
index b3f67e8..3a83b1b 100644
--- a/server/site_tests/telemetry_AFDOGenerate/telemetry_AFDOGenerate.py
+++ b/server/site_tests/telemetry_AFDOGenerate/telemetry_AFDOGenerate.py
@@ -79,15 +79,18 @@
 TELEMETRY_AFDO_BENCHMARKS = (
         # page_cycler tests are deprecated. Replace them with loading.desktop.
         ('loading.desktop', ('--pageset-repeat=1',
-                             '--story-tag-filter=typical')),
+                             '--story-tag-filter=typical',
+                             '--legacy-json-trace-format')),
         ('loading.desktop', ('--pageset-repeat=1',
-                             '--story-tag-filter=intl_ja_zh')),
+                             '--story-tag-filter=intl_ja_zh',
+                             '--legacy-json-trace-format')),
         ('rendering.desktop',
          ('--story-tag-filter=tough_canvas',
-          '--story-filter="bouncing\\*\\|canvas\\*\\|microsoft\\*"')),
-        ('octane', ),
-        ('kraken', ),
-        ('speedometer2', ),
+          '--story-filter="bouncing\\*\\|canvas\\*\\|microsoft\\*"',
+          '--legacy-json-trace-format')),
+        ('octane', ('--legacy-json-trace-format')),
+        ('kraken', ('--legacy-json-trace-format')),
+        ('speedometer2', ('--legacy-json-trace-format')),
 )
 
 # Temporarily disable this benchmark because it is failing a