Complete Timeline View

[DaveShuckerow]

Reference screenshot:

[kenzieschmoll]

Items remaining

Required:

• [x] Add timeline grid (timestamps and lines) over flame chart (done in https://github.com/flutter/devtools/pull/1624)
• [x] Port Bottom Up profiler view (done in https://github.com/flutter/devtools/pull/1659)

Nice to have:

• [ ] Implement scroll to zoom (zoom is possible via WASD currently) (https://github.com/flutter/devtools/issues/1600)
• [x] implement import/export (done in https://github.com/flutter/devtools/pull/1644)
• [ ] Tree table polish https://github.com/flutter/devtools/issues/1657

[kenzieschmoll]

Closing as the required items are complete and the 2 remaining "nice to have"s will be tracked separately for M16