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/include/dawn_native/D3D12Backend.h

@@ -22,7 +22,7 @@
 #include <windows.h>
 
 namespace dawn_native { namespace d3d12 {
-    DAWN_NATIVE_EXPORT void Init(dawnProcTable* procs, dawnDevice* device);
+    DAWN_NATIVE_EXPORT dawnDevice CreateDevice();
 
     DAWN_NATIVE_EXPORT dawnSwapChainImplementation CreateNativeSwapChainImpl(dawnDevice device,
                                                                              HWND window);

src/include/dawn_native/DawnNative.h

@@ -0,0 +1,28 @@
+// 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.
+
+#ifndef DAWNNATIVE_DAWNNATIVE_H_
+#define DAWNNATIVE_DAWNNATIVE_H_
+
+#include <dawn/dawn.h>
+#include <dawn_native/dawn_native_export.h>
+
+namespace dawn_native {
+
+    // Backend-agnostic API for dawn_native
+    DAWN_NATIVE_EXPORT dawnProcTable GetProcs();
+
+}  // namespace dawn_native
+
+#endif  // DAWNNATIVE_DAWNNATIVE_H_

src/include/dawn_native/MetalBackend.h

@@ -23,9 +23,7 @@
 #import <QuartzCore/CAMetalLayer.h>
 
 namespace dawn_native { namespace metal {
-    DAWN_NATIVE_EXPORT void Init(id<MTLDevice> metalDevice,
-                                 dawnProcTable* procs,
-                                 dawnDevice* device);
+    DAWN_NATIVE_EXPORT dawnDevice CreateDevice(id<MTLDevice> metalDevice);
     DAWN_NATIVE_EXPORT void SetNextDrawable(dawnDevice device, id<CAMetalDrawable> drawable);
     DAWN_NATIVE_EXPORT void Present(dawnDevice device);
 }}  // namespace dawn_native::metal

src/include/dawn_native/NullBackend.h

@@ -19,7 +19,7 @@
 #include <dawn_native/dawn_native_export.h>
 
 namespace dawn_native { namespace null {
-    DAWN_NATIVE_EXPORT void Init(dawnProcTable* procs, dawnDevice* device);
+    DAWN_NATIVE_EXPORT dawnDevice CreateDevice();
 }}  // namespace dawn_native::null
 
 #endif  // DAWNNATIVE_NULLBACKEND_H_

src/include/dawn_native/OpenGLBackend.h

@@ -19,9 +19,7 @@
 #include <dawn_native/dawn_native_export.h>
 
 namespace dawn_native { namespace opengl {
-    DAWN_NATIVE_EXPORT void Init(void* (*getProc)(const char*),
-                                 dawnProcTable* procs,
-                                 dawnDevice* device);
+    DAWN_NATIVE_EXPORT dawnDevice CreateDevice(void* (*getProc)(const char*));
 }}  // namespace dawn_native::opengl
 
 #endif  // DAWNNATIVE_OPENGLBACKEND_H_

src/include/dawn_native/VulkanBackend.h

@@ -24,9 +24,8 @@
 #include <vector>
 
 namespace dawn_native { namespace vulkan {
-    DAWN_NATIVE_EXPORT void Init(dawnProcTable* procs,
-                                 dawnDevice* device,
-                                 const std::vector<const char*>& requiredInstanceExtensions);
+    DAWN_NATIVE_EXPORT dawnDevice
+    CreateDevice(const std::vector<const char*>& requiredInstanceExtensions);
 
     DAWN_NATIVE_EXPORT VkInstance GetInstance(dawnDevice device);