base: Make TaskQueue a typedef instead of a subclass

Subclassing STL types is bad. And std::queue::swap exists as of c++11.

R=vmpstr

Review-Url: https://codereview.chromium.org/2068833003
Cr-Commit-Position: refs/heads/master@{#400006}
3 files changed