Support internal pipelines for Dawn

Like copyTextureCHROMIUM in Chromium, CopyImageBitmapToTexture can use
internal pipeline to do the GPU uploading. But Dawn doesn't support
internal pipeline now.

This patch adds the first internal pipeline for Dawn and add the API
CopyTextureForBrowser to use internal pipeline to do gpu uploading.

The patch integrates very simple wgsl vertex/fragment shaders to do
simple direct blit to verify the whole system works.

BUG=dawn:465

Change-Id: I8b566af38a10eea00f7426c39e752958ef057abd
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/30960
Commit-Queue: Shaobo Yan <shaobo.yan@intel.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/InternalPipelineStore.h

@@ -0,0 +1,34 @@
+// Copyright 2020 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_INTERNALPIPELINESTORE_H_
+#define DAWNNATIVE_INTERNALPIPELINESTORE_H_
+
+#include "dawn_native/ObjectBase.h"
+#include "dawn_native/dawn_platform.h"
+
+#include <unordered_map>
+
+namespace dawn_native {
+    class RenderPipelineBase;
+    class ShaderModuleBase;
+
+    struct InternalPipelineStore {
+        Ref<RenderPipelineBase> copyTextureForBrowserPipeline;
+        Ref<ShaderModuleBase> copyTextureForBrowserVS;
+        Ref<ShaderModuleBase> copyTextureForBrowserFS;
+    };
+}  // namespace dawn_native
+
+#endif  // DAWNNATIVE_INTERNALPIPELINESTORE_H_