Extract Awakable from Waiter

mojo/edk/system/waiter.h

Index: mojo/edk/system/waiter.h
diff --git a/mojo/edk/system/waiter.h b/mojo/edk/system/waiter.h
index 03ada1664302e406c9b226c22b39d628f6b72cb3..50a613b6f84614228931fe048c65ed14e7551ddc 100644
--- a/mojo/edk/system/waiter.h
+++ b/mojo/edk/system/waiter.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
+#include "mojo/edk/system/awakable.h"
 #include "mojo/edk/system/system_impl_export.h"
 #include "mojo/public/c/system/types.h"
 
@@ -20,7 +21,7 @@ namespace system {
 // under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
 // must never call out to other objects (in particular, |Dispatcher|s). This
 // class is thread-safe.
-class MOJO_SYSTEM_IMPL_EXPORT Waiter {
+class MOJO_SYSTEM_IMPL_EXPORT Waiter : public Awakable {
  public:
   Waiter();
   ~Waiter();
@@ -57,7 +58,7 @@ class MOJO_SYSTEM_IMPL_EXPORT Waiter {
 
   // Wake the waiter up with the given result and context (or no-op if it's been
   // woken up already).
-  void Awake(MojoResult result, uint32_t context);
+  void Awake(MojoResult result, uintptr_t context) override;
 
  private:
   base::ConditionVariable cv_;  // Associated to |lock_|.
@@ -70,7 +71,7 @@ class MOJO_SYSTEM_IMPL_EXPORT Waiter {
   // This is a |uint32_t| because we really only need to store an index (for
   // |MojoWaitMany()|). But in tests, it's convenient to use this for other
   // purposes (e.g., to distinguish between different wake-up reasons).
-  uint32_t awake_context_;
+  uintptr_t awake_context_;
 
   DISALLOW_COPY_AND_ASSIGN(Waiter);
 };