core: Implement vtrace (part 1 of many)

In this CL I add a basic implementation of vtrace spans and the vtrace
store.  Also add enough functionality to collect trace data when
javascript is acting as a client.

There are many shortcomings which will be addressed by future CLs.
- The store always collects, there is no pattern based collection as in go.
- JS servers never return trace information
- There is no interface to dump traces from the console / etc.

MultiPart: 2/4
Change-Id: Ia476f4f8929889f890e43a09fb29958d0dd3daa8
2 files changed
tree: b5dfb8adb21031d535ed74d6345b53ff1136c345
  1. lib/
  2. profiles/
  3. runtimes/
  4. security/
  5. services/
  6. tools/