[kernel][tracing] Add thread priorities to context switch record

ZX-2066 #done

Change-Id: I7adae307bbb6262d0f4c03299359d77a516e22d6

[tracing] Implement support for blobs

Change-Id: Ia32323954671adae397f71809cc087c403fdb0bb

[unittest] Make "msg" argument optional for {ASSERT,EXPECT}_STR_{EQ,NE}()

This makes ASSERT/EXPECT_STR_EQ() consistent with the numeric
comparison checks such as EXPECT_EQ(), where the "msg" argument is
already optional.

Simplify some tests by using EXPECT_STR_EQ() directly instead of
defining an EXPECT_CSTR_EQ() helper.

Change-Id: Ia6e697a7492d16b86efe92a4e51c0ecc82749ed2

[unittest] Remove 'length' argument from EXPECT_STR_EQ()/ASSERT_STR_EQ()

The 'length' argument is redundant now that these two functions always
compare the whole strings.

I updated the call sites using an automated tool.

I've removed the now-unneeded EXPECT_STRING_EQ() wrapper in
syslog_socket_tests.cpp.

Change-Id: I80fff5c5ccdc44337125bc2b2d3386fc6606f1dc

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[zircon][mxtl->fbl] Rename mxtl to fbl

Change-Id: Ie21b6498e1bfb0a7fa0315e40b9e5c3ee78646be

[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