Introduce mojo interface for collecting StackSamplingProfiler data
Adds interfaces, typemaps, and tests for collecting
StackSamplingProfiler result types. The collection interface will be
used to receive stack profiles from non-browser processes.
BUG=
517958
Committed:
https://crrev.com/551e14b666639639850b2de5588b30b4e40d626b
Cr-Commit-Position: refs/heads/master@{#412963}