dawn_native: Factor getting procs into a single function.

Now the backends only expose the creation of devices. Getting the procs
is moved to DawnNative that will over time more backend-agnostic APIs.

src/dawn_native/DawnNative.cpp

@@ -0,0 +1,27 @@
+// Copyright 2018 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "dawn_native/DawnNative.h"
+
+// Contains the entry-points into dawn_native
+
+namespace dawn_native {
+
+    dawnProcTable GetProcsAutogen();
+
+    dawnProcTable GetProcs() {
+        return GetProcsAutogen();
+    }
+
+}  // namespace dawn_native