EDK: Make mojo::embedder::AsyncWait (etc.) take an std::function instead of a base::Callback.

mojo/edk/system/async_waiter.h

Index: mojo/edk/system/async_waiter.h
diff --git a/mojo/edk/system/async_waiter.h b/mojo/edk/system/async_waiter.h
index 9dece06e5f2f8a1919d54d0ffecf0282f886a6df..35a72f4239c1b793b590ae1a03bf9bd9c66b47e6 100644
--- a/mojo/edk/system/async_waiter.h
+++ b/mojo/edk/system/async_waiter.h
@@ -5,7 +5,8 @@
 #ifndef MOJO_EDK_SYSTEM_ASYNC_WAITER_H_
 #define MOJO_EDK_SYSTEM_ASYNC_WAITER_H_
 
-#include "base/callback.h"
+#include <functional>
+
 #include "mojo/edk/system/awakable.h"
 #include "mojo/public/c/system/types.h"
 #include "mojo/public/cpp/system/macros.h"
@@ -16,7 +17,7 @@ namespace system {
 // An |Awakable| implementation that just calls a given callback object.
 class AsyncWaiter final : public Awakable {
  public:
-  using AwakeCallback = base::Callback<void(MojoResult)>;
+  using AwakeCallback = std::function<void(MojoResult)>;
 
   // |callback| must satisfy the same contract as |Awakable::Awake()|.
   explicit AsyncWaiter(const AwakeCallback& callback);