Update mojo sdk to rev f6c8ec07c01deebc13178d516225fd12695c3dc2

mojo/public/mojo.gni

Index: mojo/public/mojo.gni
diff --git a/mojo/public/mojo.gni b/mojo/public/mojo.gni
index 5cff440f9063f5c04ab563e5a56c1eb98fbb60c8..b310260b0856eef147b82fea38e2c1ff918a82e2 100644
--- a/mojo/public/mojo.gni
+++ b/mojo/public/mojo.gni
@@ -10,3 +10,9 @@ declare_args() {
   # Whether to build the dart bindings.
   mojo_use_dart = false
 }
+
+# The absolute path to the directory containing the mojo public SDK (i.e., the
+# directory containing mojo/public). The build files within the Mojo public
+# SDK use this variable to allow themselves to be parameterized by the location
+# of the public SDK within a client repo.
+mojo_root = get_path_info("../..", "abspath")