[gn] Configure trace_events for v8 stand-alone

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 97bb7a3beb47b00863af238527401940e03d7613..6b2408e3f15da55234a5a33608a3b7dde7e9f32e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -721,8 +721,7 @@ v8_source_set("v8_base") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
 
   sources = [
-    # TODO(fmeawad): This needs to be updated to support standalone V8 builds.
-    "../base/trace_event/common/trace_event_common.h",
+    "//base/trace_event/common/trace_event_common.h",

[Michael Achenbach, 2016/05/24 12:17:53]

// refers to the project root. Both chromium and v8 stand-alone deps trace_event
into the location: root/base/trace_event/..., where root is either src or v8.

[Nico, 2016/08/03 19:17:31]

Projects outside of src.git must not depend on base, else it becomes impossible
to change. Say we wanted to rename base/...trace_event_common.h in src. We
currently can't 'cause this file refers to it but it lives in v8.

Please find a way to do what you want to do without having v8 implicitly depend
on base.

     "include/v8-debug.h",
     "include/v8-experimental.h",
     "include/v8-platform.h",