Move tracing_impl code to mojo/common

mojo/common/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//mojo/public/tools/bindings/mojom.gni")
+
 # GYP version: mojo/mojo_base.gyp:mojo_common_lib
 component("common") {
   output_name = "mojo_common_lib"
 
   sources = [
     "common_type_converters.cc",
     "common_type_converters.h",
     "data_pipe_utils.cc",
     "data_pipe_utils.h",
     "handle_watcher.cc",
@@ skipping 35 matching lines @@
     "//mojo/edk/test:run_all_unittests",
     "//mojo/edk/test:test_support",
     "//mojo/environment:chromium",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/system",
     "//mojo/public/cpp/test_support:test_utils",
     "//testing/gtest",
     "//url",
   ]
 }
+
+source_set("tracing_impl") {
+  sources = [
+    "tracing_impl.cc",
+    "tracing_impl.h",
+  ]
+
+  deps = [
+    ":tracing_bindings",
+    "//base",
+    "//mojo/public/cpp/bindings",
+  ]
+}
+
+mojom("tracing_bindings") {
+  sources = [ "tracing.mojom" ]
+}