[BlobAsync] Faster shortcuttin, make renderer controller leaky & alive.

This should fix strange memory access crashes observed in the
following bugs by doing the following things:
1. We make the controller a leaky lazy instance so it isn't destructed.
2. We make one less message loop hop before we call AddProcessRef, so
   hopefully our process won't be shutting down in the middle of a
   transfer.
3. We send the 'descriptions' as early as possible if we're below the
   IPC threshold, which should help some of the speed regressions.
4. We prevent sudden shutdowns (like tab bar closing) by using
   blink::Platform::current()->suddenTerminationChanged(false);

BUG=600462,600435,599490,599416,375297

Review URL: https://codereview.chromium.org/1853333003

Cr-Commit-Position: refs/heads/master@{#385472}
11 files changed