Remove glad and replace it with our own GL header

This completely removes the dependency on glad by generating the GL
headers from gl.xml directly.

This requires adding khrplatform.h so all Khronos dependencies are
gathered in third_party/khronos.

Also removes a stray CMakeLists.txt that was still hanging out.

BUG=dawn:165

Change-Id: Ia64bc51bc8b18c6b48613918e2f309f7405ecb3b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/8163
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/opengl/BufferGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/Buffer.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/ComputePipelineGL.h

@@ -19,7 +19,7 @@
 
 #include "dawn_native/opengl/PipelineGL.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/NativeSwapChainImplGL.h

@@ -18,7 +18,7 @@
 #include "dawn_native/OpenGLBackend.h"
 
 #include "dawn_native/dawn_platform.h"
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/PersistentPipelineStateGL.h

@@ -16,8 +16,7 @@
 #define DAWNNATIVE_OPENGL_PERSISTENTPIPELINESTATEGL_H_
 
 #include "dawn_native/dawn_platform.h"
-
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/PipelineGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/Pipeline.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 #include <vector>
 

src/dawn_native/opengl/PipelineLayoutGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/PipelineLayout.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/RenderPipelineGL.h

@@ -18,8 +18,7 @@
 #include "dawn_native/RenderPipeline.h"
 
 #include "dawn_native/opengl/PipelineGL.h"
-
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 #include <vector>
 

src/dawn_native/opengl/SamplerGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/Sampler.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/ShaderModuleGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/ShaderModule.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/SwapChainGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/SwapChain.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/TextureGL.h

@@ -17,7 +17,7 @@
 
 #include "dawn_native/Texture.h"
 
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/UtilsGL.h

@@ -16,7 +16,7 @@
 #define DAWNNATIVE_OPENGL_UTILSGL_H_
 
 #include "dawn_native/dawn_platform.h"
-#include "glad/glad.h"
+#include "dawn_native/opengl/opengl_platform.h"
 
 namespace dawn_native { namespace opengl {
 

src/dawn_native/opengl/opengl_platform.h

@@ -0,0 +1,15 @@
+// Copyright 2019 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/opengl/opengl_platform_autogen.h"