Reland "Rerouting all Java tasks through TaskRunner API"

This is a reland of 8e470e32ba80f52073bd3a8cfe2c038675034d9b

Original change's description:
> Rerouting all Java tasks through TaskRunner API
> 
> Pre-native Java tasks are now having their priority set when started.
> Also switches dynamicmodule's ModuleLoader to use the TaskTrait's
> priority setting instead of manually setting the thread priority.
> 
> Bug: 863457
> Change-Id: Iee601ca1e18e2637f8e930c6d212c8115e682fc3
> Reviewed-on: https://chromium-review.googlesource.com/c/1407374
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
> Reviewed-by: Andrew Grieve <agrieve@chromium.org>
> Reviewed-by: Benoit L <lizeb@chromium.org>
> Commit-Queue: Sam Maier <smaier@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#626095}

Bug: 863457
Change-Id: Icf625b8df9e8335d9f59e979a9cbf423dec1af04
Reviewed-on: https://chromium-review.googlesource.com/c/1439300
Commit-Queue: Sam Maier <smaier@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629591}
4 files changed