Implement tracing interface for v8

DEPS

 # Note: The buildbots evaluate this file with CWD set to the parent
 # directory and assume that the root of the checkout is in ./v8/, so
 # all paths in here must match this assumption.
 
 vars = {
   "git_url": "https://chromium.googlesource.com",
 }
 
 deps = {
   "v8/build/gyp":
     Var("git_url") + "/external/gyp.git" + "@" + "b85ad3e578da830377dbc1843aa4fbc5af17a192",
   "v8/third_party/icu":
     Var("git_url") + "/chromium/deps/icu.git" + "@" + "8d342a405be5ae8aacb1e16f0bc31c3a4fbf26a2",
   "v8/buildtools":
     Var("git_url") + "/chromium/buildtools.git" + "@" + "68e3c238a5ab347436762cb929316aa55ca72563",
-  # TODO(fmeawad): this dependency is not currently used. Added to allow for developement of the V8 Tracing system.
   "v8/base/trace_event/common":
     Var("git_url") + "/chromium/src/base/trace_event/common.git" + "@" + "d83d44b13d07c2fd0a40101a7deef9b93b841732",
   "v8/tools/swarming_client":
     Var('git_url') + '/external/swarming.client.git' + '@' + "9cdd76171e517a430a72dcd7d66ade67e109aa00",
   "v8/testing/gtest":
     Var("git_url") + "/external/github.com/google/googletest.git" + "@" + "6f8a66431cb592dad629028a50b3dd418a408c87",
   "v8/testing/gmock":
     Var("git_url") + "/external/googlemock.git" + "@" + "0421b6f358139f02e102c9c332ce19a33faf75be",
   "v8/test/benchmarks/data":
     Var("git_url") + "/v8/deps/third_party/benchmarks.git" + "@" + "05d7188267b4560491ff9155c5ee13e207ecd65f",
@@ skipping 140 matching lines @@
     'name': 'clang',
     'pattern': '.',
     'action': ['python', 'v8/tools/clang/scripts/update.py', '--if-needed'],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "v8/build/gyp_v8"],
   },
 ]