[Mojo] Replace empty constructors/destructors with the default implementation

Using 'default' is the modern C++ approach used by chromium, and some
analysers complain about the old style.

Bug: None
Change-Id: Ic531d39490f3005abb163830dfc312e1351b003a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2249283
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Anand K Mistry <amistry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779559}
diff --git a/mojo/core/channel_fuchsia.cc b/mojo/core/channel_fuchsia.cc
index 8ca1055..3154091 100644
--- a/mojo/core/channel_fuchsia.cc
+++ b/mojo/core/channel_fuchsia.cc
@@ -108,7 +108,7 @@
     return *this;
   }
 
-  ~MessageView() {}
+  ~MessageView() = default;
 
   const void* data() const {
     return static_cast<const char*>(message_->data()) + offset_;