Add new tracing category 'v8.stack_trace'

Various places in Chromium collect and symbolize V8 stack traces.
This could be DevTools or heavy ads instrumentation. To get better
insights we want to add some trace events around stack trace
capturing and symbolization under a new, disabled by default, tracing
category.

Corresponding V8 CL: https://crrev.com/c/2491028

R=petermarshall@chromium.org

Change-Id: I266b0783dcf6266efc512503b7b13044bd8b71c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490044Reviewed-by: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819793}

base/trace_event/builtin_categories.h

@@ -241,6 +241,7 @@
   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.stack_trace"))                         \
   X(TRACE_DISABLED_BY_DEFAULT("v8.turbofan"))                            \
   X(TRACE_DISABLED_BY_DEFAULT("v8.wasm.detailed"))                       \
   X(TRACE_DISABLED_BY_DEFAULT("video_and_image_capture"))                \