Replace TaskType::kUnspecedTimer with kInternalUserInteraction where inputing is related

We plan to eliminate kUnthrottled, kUnspecedTimer and kUnspecedLoading
and replace them with appropriate kInternal* task types.

This CL also introduces a new TaskType kInternalUserInteraction for
future usage.

Bug: 830489
Change-Id: I5d2852c1e96c2955d1e2c2368da80d44cb57b846
Reviewed-on: https://chromium-review.googlesource.com/1005135
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549735}
7 files changed