Rename namespace dawn_platform to dawn::platform.

But keep a namespace alias to avoid breaking project that depend on the
previous namespace name while they get updated.

Some TraceEvent.h macro were using "platform" as an argument name so
that was renamed to "platformObj" to avoid conflicting with ::platform::

Bug: dawn:824
Change-Id: Iaf14853f02b0d9fcf866ce87788f87a3fdf8f364
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/75541
Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/include/dawn_native/DawnNative.h

@@ -22,9 +22,9 @@
 #include <string>
 #include <vector>
 
-namespace dawn_platform {
+namespace dawn::platform {
     class Platform;
-}  // namespace dawn_platform
+}  // namespace dawn::platform
 
 namespace wgpu {
     struct AdapterProperties;
@@ -193,7 +193,7 @@ namespace dawn_native {
         // Enable debug capture on Dawn startup
         void EnableBeginCaptureOnStartup(bool beginCaptureOnStartup);
 
-        void SetPlatform(dawn_platform::Platform* platform);
+        void SetPlatform(dawn::platform::Platform* platform);
 
         // Returns the underlying WGPUInstance object.
         WGPUInstance Get() const;

src/include/dawn_platform/DawnPlatform.h

@@ -23,7 +23,7 @@
 
 #include <dawn/webgpu.h>
 
-namespace dawn_platform {
+namespace dawn::platform {
 
     enum class TraceCategory {
         General,     // General trace events
@@ -111,6 +111,8 @@ namespace dawn_platform {
         Platform& operator=(const Platform&) = delete;
     };
 
-}  // namespace dawn_platform
+}  // namespace dawn::platform
+
+namespace dawn_platform = dawn::platform;
 
 #endif  // DAWNPLATFORM_DAWNPLATFORM_H_