GitLab

In the resource_prefetch_predictor, the maximum number of concurrent
prefetches is set to 24. This is too high, as:
- It defeats the prioritization of resources in the database
- It was shown to slow down page loads in some case on slow connections
  by starving the page load resource fetches. (local testing using WPR
  and tools in tools/resource_prefetch_predictor)

BUG=631966,655980

Review-Url: https://codereview.chromium.org/2589713002
Cr-Commit-Position: refs/heads/master@{#439453}