Measure concurrent load requests

[0nko]

Task/Issue URL:

Description

The PR adds a counter that measures all concurrent load requests across all BrowserWebViewClient instances. It uses AtomicInteger and ConcurrentHashMap to track the requests in progress and the count is reported to the PageLoadedHandler.

For the counter, there's a 30s time-out (maybe it should be longer?) so that we don't count requests that never finish.

Steps to test this PR

Add ### to the logcat filter to see the counter logs or $$$ to see the page load logs.

• Enable swipingTabs feature flag
• Make sure you have a couple of tabs in the browser
• Start the app
• Try loading a tab without swiping
• Verify that there are 0 concurrent load requests reported
• Swipe fast a couple of times between tabs
• Notice that the concurrent tab requests are reported