Add "v8.turbofan" trace event category.

The category was introduced in V8 as part of

  https://chromium-review.googlesource.com/1538135

and is used for detailed trace events of the TurboFan optimizing
compiler. It should be listed here alongside the other V8 events
for a better user experience.

Bug: v8:8598, v8:9039
Change-Id: I2ac267af2083fb724e9e524a8e9ddfb6ba6b5611
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539843
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644514}

base/trace_event/builtin_categories.h

@@ -206,6 +206,7 @@
   X(TRACE_DISABLED_BY_DEFAULT("v8.runtime"))                             \
   X(TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats"))                       \
   X(TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats_sampling"))              \
+  X(TRACE_DISABLED_BY_DEFAULT("v8.turbofan"))                            \
   X(TRACE_DISABLED_BY_DEFAULT("v8.wasm"))                                \
   X(TRACE_DISABLED_BY_DEFAULT("video_and_image_capture"))                \
   X(TRACE_DISABLED_BY_DEFAULT("viz.debug.overlay_planes"))               \