Mojo: Move platform handle/channel stuff in system to embedder namespace.

mojo/system/scoped_platform_handle.h

Index: mojo/system/scoped_platform_handle.h
diff --git a/mojo/system/scoped_platform_handle.h b/mojo/system/scoped_platform_handle.h
index 55be0a11c94d2a46bb4548316b9e4e318a83e26d..9320a82e2686469a7e3d2d151fd95fff587a212a 100644
--- a/mojo/system/scoped_platform_handle.h
+++ b/mojo/system/scoped_platform_handle.h
@@ -11,7 +11,7 @@
 #include "mojo/system/system_impl_export.h"
 
 namespace mojo {
-namespace system {
+namespace embedder {
 
 class MOJO_SYSTEM_IMPL_EXPORT ScopedPlatformHandle {
   MOVE_ONLY_TYPE_FOR_CPP_03(ScopedPlatformHandle, RValue);
@@ -55,7 +55,7 @@ class MOJO_SYSTEM_IMPL_EXPORT ScopedPlatformHandle {
   PlatformHandle handle_;
 };
 
-}  // namespace system
+}  // namespace embedder
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_SCOPED_PLATFORM_HANDLE_H_