Mojo: Convert OVERRIDE -> override in mojo/{embedder,system}.

mojo/embedder/simple_platform_support.h

Index: mojo/embedder/simple_platform_support.h
diff --git a/mojo/embedder/simple_platform_support.h b/mojo/embedder/simple_platform_support.h
index 899c0271bd2cf00e48d81352bfe74e73d3a6c232..07396af4cad9be3e58873235cedc3fa6366eda63 100644
--- a/mojo/embedder/simple_platform_support.h
+++ b/mojo/embedder/simple_platform_support.h
@@ -22,10 +22,10 @@ class MOJO_SYSTEM_IMPL_EXPORT SimplePlatformSupport : public PlatformSupport {
   SimplePlatformSupport() {}
   virtual ~SimplePlatformSupport() {}
 
-  virtual PlatformSharedBuffer* CreateSharedBuffer(size_t num_bytes) OVERRIDE;
+  virtual PlatformSharedBuffer* CreateSharedBuffer(size_t num_bytes) override;
   virtual PlatformSharedBuffer* CreateSharedBufferFromHandle(
       size_t num_bytes,
-      ScopedPlatformHandle platform_handle) OVERRIDE;
+      ScopedPlatformHandle platform_handle) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SimplePlatformSupport);