src: Update trace event macros to V8 5.7 version

src/tracing/trace_event.h was updated by applying the following changes:

1) Include src/tracing/trace_event_common.h instead of the one from v8
base.

2) Replace all instances of base::Atomic with intptr_t (trace events can
only be generated from the main thread for now).

3) Replace instances of V8_INLINE with inline.

4) Eliminate uses of DCHECK.

5) Eliminate uses of V8_UNLIKELY, the branch predictor should be good
enough alone.

6) Change the namespace used by trace_event.h from v8::internal::tracing
to node::tracing.

7) Remove CallStatsScopedTracer class and related macros (they rely on
V8 implementation details).

8) Change ConvertableToTraceFormat to v8::ConvertableToTraceFormat.

9) Add function "static void SetCurrentPlatform(v8::Platform*
platform);" to the declaration of TraceEventHelper.