When we use unique_ptr on tracing controller and release it to platform,
unique_ptr will crash when we try to start tracing with trace config, this patch
replaces it with raw pointer and delete it explicitly at the end when needed.

TBR=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2488003002
Cr-Commit-Position: refs/heads/master@{#40871}