gn: Add all v8 targets to gn_all

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 35610ce68b48ff1294c3f9b1546440cb89a10afd..df1dc2b2da85af9f8546a8f240d2e5e88861bff4 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -784,6 +784,8 @@ group("gn_mojo_targets") {
 }
 
 group("gn_visibility") {
+  testonly = true

[Michael Achenbach, 2016/06/03 15:17:17]

Not sure about marking this testonly. If I don't I need to put v8:gn_all
somewhere else as  it's testonly.

[Dirk Pranke, 2016/06/03 18:14:54]

Marking this testonly is probably fine.

+
   deps = [
     "//build/config/sanitizers:options_sources",
     # "//third_party/pdfium:pdfium_embeddertests",  # TODO(GYP): visibility?
@@ -792,6 +794,7 @@ group("gn_visibility") {
 
   if (!is_ios) {
     deps += [
+      "//v8:gn_all",

[Dirk Pranke, 2016/06/03 18:14:54]

This almost certainly shouldn't be part of "gn_visibility", since the purpose of
this target it to reference only targets that are not otherwise visibile, but
are pulled in by "all".

I think this should probably be a dependency of either ":gn_all", or
":both_gn_and_gyp", or ":gn_only". Ideally it should be one of the latter two,
depending on whether it references targets that exist in both or targets that
exist only in GN. 

If it references a mixture, then it's fine to use gn_all instead.

       "//v8:postmortem-metadata",
       "//v8:v8_snapshot",
     ]