[trace-engine] Send a signal for STOPPING->STOPPED state change

Tested: /boot/test/sys/trace-test, passes with new test
Change-Id: Icffa0fdc7def54ff65a4c00c67ae6742e627f5e5

[trace-engine] Only try to release prolonged context if acquired.

Tested: /boot/test/sys/trace-test
New test crashes without patch, passes with patch.

DX-441 #done

Change-Id: If54642270dc4eba8c008b920feee2b8aeb04df97

[tracing] Add support for circular and streaming modes

Tested:
/boot/test/sys/trace-test
trace-benchmark
Further testing done on the garnet side.

Change-Id: I8ec21ba0adc57d090bbfe4be6d56fc695aa645d4

[tracing] Add beginnings of trace buffering mode support

This patch just adds the basic infrastructure.
Support for circular and streaming modes comes later.

Tested:
/system/test/sys/trace-test
trace record --buffering-mode=oneshot \
--categories=stress:example,stress:something \
/system/bin/trace-stress --count=5000
trace record --buffering-mode=circular \
--categories=stress:example,stress:something \
/system/bin/trace-stress --count=5000
[trace will be empty, but should run]
trace record --buffering-mode=streaming \
--categories=stress:example,stress:something \
/system/bin/trace-stress --count=5000
[trace will be empty, but should run]

Change-Id: I1fc28668dee652c88df9d5e669c8b4ac978604bc

[utest][trace] Export ability to squelch trace output

The code provides a nice means to squash things like timestamps
so that they don't interfere when being compared with an expected
output string. This patch just makes this functionality more
easily accessible, for later use in circular and streaming testcases.

Change-Id: I68c5a6f8515ddc76da84435ba1b5b181418944e4
Tested: /boot/test/sys/trace-test

[tracing] Add support for compilation of C clients at -O0

DX-329 #done

Tested: /boot/test/sys/trace-test
New testcase added to verify compilation at -O0.

Change-Id: I5151e1f2f1fc9d5bbe9d0b81fde2497c88ff8fa0

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[trace] Port Fuchsia tracing system to Magenta.

The Fuchsia tracing system supports instrumentation of userspace
programs to collect trace records.

This implementation consists of...

- libtrace: a static library providing C and C++ instrumentation macros
and functions designed to be linked into client programs
- libtrace-engine: a shared library with a C ABI which manages
global tracing state in the process and provides
functions to write trace records
- libtrace-provider: a static library which implements the TraceProvider
FIDL interface and registers an instrumented
program with the trace manager
- libtrace-reader: a static library which provides a C++ API for reading
binary trace data
- unit tests
- benchmarks
- documentation

This is almost a complete rewrite of the code formerly in //apps/tracing
but it remains compatible with the trace format and preserves most of
the structure of the trace event API.

The main differences are...

- The <trace/event.h> API uses identical syntax for C and C++ with
a few extra goodies for C++ type inference.
- The trace engine is factored out as a shared library with a C ABI
instead of being written as a C++ static library, this makes it more
suitable for instrumentation of libraries and device drivers.
- The API is extensively documented.
- We actually have benchmarks to measure instrumentation overhead.

There are still a few pieces left in //apps/tracing, such as the trace
manager and command-line tools, which will be moved over later.

Change-Id: I2d2986be0e63e5aa21fe56dd03024490b0334214