Steps to reproduce:

1) Open Chrome

2) Open the Chrome devtools, enter console.log("123"). (This weird step makes it so that the blink.console tracing category appears) 

3) Navigate to chrome:tracing

4) Click Record, select the following categories necessary for the loading metrics to work correctly (https://cs.chromium.org/chromium/src/tools/perf/benchmarks/loading_metrics_category.py?type=cs&q=augmentoptionsforloading&sq=package:chromium&g=0&l=6)

  - blink.console
  - navigation
  - blink.user_timing
  - loading
  - toplevel
  - disabled-by-default-network

5) Click "record" in the dialog to start the trace

6) Open wikipedia.org in another tab and wait 10 seconds to reach "interactive"

7) Tab back to chrome:tracing (without closing wikipedia) and click stop

8) Click on the metrics side panel and select loadingMetric

EXPECTED: loadingMetric contains all timeToX events and their breakdowns

ACTUAL: loadingMetric contains only the timeToOnload event. Opening up the trace locally reveals that the trace does in fact have events like firstMeaningfulPaintCandidate in it, but those aren't actually be interpreted by the loadingMetric.

This appears to only be a problem with interactive traces: the benchmarks still seem to be running fine.