Add ppapi, improve Windows GN build.

gpu/ipc/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.
 
-source_set("tracing") {
+source_set("ipc") {
   sources = [
-    "child_trace_message_filter.cc",
-    "child_trace_message_filter.h",
-    "tracing_messages.cc",
-    "tracing_messages.h",
+    "gpu_command_buffer_traits.cc",
+    "gpu_command_buffer_traits.h",
   ]
 
+  configs += [ "//third_party/khronos:khronos_headers" ]
+
   deps = [
-    "//base",
+    "//gpu/command_buffer/common",
     "//ipc",
   ]
 }