Thank you for reporting!

The /graph_json request hits the 60s timeout in _UpdateRevisionMap > GetLatestRowsForTest, which runs a small Row query.
The problem is that the frontend is trying to load data for all 500+ test cases at once. If you select a single test case, it loads quickly:
https://chromeperf.appspot.com/report?sid=53ce524ae8a1fd549cb7b940dba78382f816d9a9a38191a716e5b4b9c8e583cd

Even if it successfully loaded 500 timeseries, the graph would be an unintelligible mess. The next thing you would do is certainly deselect all of them and try a few.
I can make the frontend limit the number of subtests that it requests to only the first 10 (or maybe 100?) by default, though that's probably still not the right UX.

In v2spa, the summary timeseries (data merged across all test cases) loads in <2s for me:
https://v2spa-dot-chromeperf.appspot.com/#testSuite=rendering.desktop&measurement=thread_total_all_cpu_time_per_frame&bot=ChromiumPerf%253Amac-10_12_laptop_low_end-perf
You can click the "Test cases" tab below the chart for sparklines for all 500+ test cases. It will start displaying them within a few seconds, though it will take a minute or two to finish loading all of them. (The backend timed out for a few of them for me. I'll look into fixing that, but it's not a big problem because they all loaded when I refreshed the tab.) After the data for all test cases is fetched, it's cached in the service worker, so you can quickly investigate groups of a few test cases at a time by selecting Tags in the Test cases menu then "All test cases"; it will quickly merge the timeseries for the selected test cases. You can toggle the Aggregate checkbox below the Test cases menu to display the separate timeseries for each test case.

Please try v2spa and let me know how it works for you!

skobes: Please reopen if v2spa doesn't help.

Thanks Ben, your explanation makes sense to me.  I didn't realize I was missing a test case.