Increase 10s timeout on tracing tests to 15s

We have seen more timeouts recently, which is probably in part because
the functionality of the engine has been extended. Let's see if a higher
limit increases stability on the bots.

Bug: none
Change-Id: I8eade981a07865bd4d2f0d3a18c7cd88218c20c8
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6415797
Reviewed-by: Eric Leese <leese@chromium.org>
Commit-Queue: Jack Franklin <jacktfranklin@chromium.org>
Commit-Queue: Eric Leese <leese@chromium.org>
Auto-Submit: Jack Franklin <jacktfranklin@chromium.org>

Author: jackfranklin

front_end/testing/TraceLoader.ts

@@ -58,7 +58,7 @@ export class TraceLoader {
     if (!context || context.timeout() >= 10_000) {
       return;
     }
-    context.timeout(10_000);
+    context.timeout(15_000);
   }
 
   /**