Add method table to CPU profiler

[kenzieschmoll]

Observatory has a method table view for cpu profiles. The table shows the list of methods with their consumption percentages. It also shows a table of callees and callers.

[escamoteur]

This would be extremely helpful to detect bottlenecks. Especially such a view should also show the number a function is called and its total time that it is used.
It would be good if it could list min,max and average time a method takes.

Here it would be helpful if we got functions in dart to start stop the sampling to analyse just a segment of out App.

[kenzieschmoll]

Thanks for the feedback! Tracking issue for programatic start / stop here: #947.

[kenzieschmoll]

Here is the source from observatory for the method table: https://github.com/dart-lang/sdk/blob/main/runtime/observatory/lib/src/elements/cpu_profile_table.dart

code for forming the CPU profile tree: https://github.com/dart-lang/sdk/blob/main/runtime/observatory/lib/src/sample_profile/sample_profile.dart