Standardize usage of virtual/override/final in mojo/

mojo/edk/embedder/simple_platform_support.h

Index: mojo/edk/embedder/simple_platform_support.h
diff --git a/mojo/edk/embedder/simple_platform_support.h b/mojo/edk/embedder/simple_platform_support.h
index fc5371deb12b187321a18de7bb40152dcc9b24f2..2013f8dc637db60043a1b7eb19163406a6a9db05 100644
--- a/mojo/edk/embedder/simple_platform_support.h
+++ b/mojo/edk/embedder/simple_platform_support.h
@@ -20,10 +20,10 @@ namespace embedder {
 class MOJO_SYSTEM_IMPL_EXPORT SimplePlatformSupport : public PlatformSupport {
  public:
   SimplePlatformSupport() {}
-  virtual ~SimplePlatformSupport() {}
+  ~SimplePlatformSupport() override {}
 
-  virtual PlatformSharedBuffer* CreateSharedBuffer(size_t num_bytes) override;
-  virtual PlatformSharedBuffer* CreateSharedBufferFromHandle(
+  PlatformSharedBuffer* CreateSharedBuffer(size_t num_bytes) override;
+  PlatformSharedBuffer* CreateSharedBufferFromHandle(
       size_t num_bytes,
       ScopedPlatformHandle platform_handle) override;