Add dawn_platform::Platform for handling tracing events in Dawn

This patch provides Chromium TRACE_EVENT macros and hooks for
implementing the TRACE_EVENT api.

Bug: chromium:958013
Change-Id: I033b1c7ca57c550504a1bea1898a1a152831922b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/7060
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

src/include/dawn_native/DawnNative.h

@@ -21,6 +21,10 @@
 #include <string>
 #include <vector>
 
+namespace dawn_platform {
+    class Platform;
+}  // namespace dawn_platform
+
 namespace dawn_native {
 
     struct PCIInfo {
@@ -140,6 +144,9 @@ namespace dawn_native {
         void EnableBeginCaptureOnStartup(bool beginCaptureOnStartup);
         bool IsBeginCaptureOnStartupEnabled() const;
 
+        void SetPlatform(dawn_platform::Platform* platform);
+        dawn_platform::Platform* GetPlatform() const;
+
       private:
         InstanceBase* mImpl = nullptr;
     };

src/include/dawn_platform/DawnPlatform.h

@@ -0,0 +1,46 @@
+// 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.
+
+#ifndef DAWNPLATFORM_DAWNPLATFORM_H_
+#define DAWNPLATFORM_DAWNPLATFORM_H_
+
+#include <dawn_native/dawn_native_export.h>
+
+#include <stdint.h>
+
+namespace dawn_platform {
+
+    class DAWN_NATIVE_EXPORT Platform {
+      public:
+        virtual ~Platform() {
+        }
+        virtual const unsigned char* GetTraceCategoryEnabledFlag(const char* name) = 0;
+
+        virtual double MonotonicallyIncreasingTime() = 0;
+
+        virtual uint64_t AddTraceEvent(char phase,
+                                       const unsigned char* categoryGroupEnabled,
+                                       const char* name,
+                                       uint64_t id,
+                                       double timestamp,
+                                       int numArgs,
+                                       const char** argNames,
+                                       const unsigned char* argTypes,
+                                       const uint64_t* argValues,
+                                       unsigned char flags) = 0;
+    };
+
+}  // namespace dawn_platform
+
+#endif  // DAWNPLATFORM_DAWNPLATFORM_H_