[tracing] Turn StackFrame into struct.
This change turns StackFrame (aka const char*) into a struct and
introduces 'type' field which controls how stack frame is formatted
when it's written to trace file. As an example, thread name, which
previously was just a string like any other function name, is now
formatted as '[Thread: %s]'.
More stack frame types will be added in the future, for example
native allocation tracing will add 'program counter' type.
BUG=602701
Review URL: https://codereview.chromium.org/1891543003
Cr-Commit-Position: refs/heads/master@{#388553}
10 files changed
