Revert of Mojo: Armed Watchers

mojo/public/c/system/thunks.h

Index: mojo/public/c/system/thunks.h
diff --git a/mojo/public/c/system/thunks.h b/mojo/public/c/system/thunks.h
index 31d22890ff820b824b8285df51e91b43d87ee365..161faf135097ec2973943bf0a85c01d4f5d0d487 100644
--- a/mojo/public/c/system/thunks.h
+++ b/mojo/public/c/system/thunks.h
@@ -13,10 +13,28 @@
 #include "mojo/public/c/system/core.h"
 #include "mojo/public/c/system/system_export.h"
 
-// Structure used to bind the basic Mojo Core functions to an embedder
-// implementation. This is intended to eventually be used as a stable ABI
-// between a Mojo embedder and some loaded application code, but for now it is
-// still effectively safe to rearrange entries as needed.
+// The embedder needs to bind the basic Mojo Core functions of a DSO to those of
+// the embedder when loading a DSO that is dependent on mojo_system.
+// The typical usage would look like:
+// base::ScopedNativeLibrary app_library(
+//     base::LoadNativeLibrary(app_path_, &error));
+// typedef MojoResult (*MojoSetSystemThunksFn)(MojoSystemThunks*);
+// MojoSetSystemThunksFn mojo_set_system_thunks_fn =
+//     reinterpret_cast<MojoSetSystemThunksFn>(app_library.GetFunctionPointer(
+//         "MojoSetSystemThunks"));
+// MojoSystemThunks system_thunks = MojoMakeSystemThunks();
+// size_t expected_size = mojo_set_system_thunks_fn(&system_thunks);
+// if (expected_size > sizeof(MojoSystemThunks)) {
+//   LOG(ERROR)
+//       << "Invalid DSO. Expected MojoSystemThunks size: "
+//       << expected_size;
+//   break;
+// }
+
+// Structure used to bind the basic Mojo Core functions of a DSO to those of
+// the embedder.
+// This is the ABI between the embedder and the DSO. It can only have new
+// functions added to the end. No other changes are supported.
 #pragma pack(push, 8)
 struct MojoSystemThunks {
   size_t size;  // Should be set to sizeof(MojoSystemThunks).
@@ -97,18 +115,11 @@
                                 MojoHandle* handles,
                                 MojoResult* results,
                                 struct MojoHandleSignalsState* signals_states);
-  MojoResult (*CreateWatcher)(MojoWatcherCallback callback,
-                              MojoHandle* watcher_handle);
-  MojoResult (*Watch)(MojoHandle watcher_handle,
-                      MojoHandle handle,
+  MojoResult (*Watch)(MojoHandle handle,
                       MojoHandleSignals signals,
+                      MojoWatchCallback callback,
                       uintptr_t context);
-  MojoResult (*CancelWatch)(MojoHandle watcher_handle, uintptr_t context);
-  MojoResult (*ArmWatcher)(MojoHandle watcher_handle,
-                           uint32_t* num_ready_contexts,
-                           uintptr_t* ready_contexts,
-                           MojoResult* ready_results,
-                           MojoHandleSignalsState* ready_signals_states);
+  MojoResult (*CancelWatch)(MojoHandle handle, uintptr_t context);
   MojoResult (*FuseMessagePipes)(MojoHandle handle0, MojoHandle handle1);
   MojoResult (*WriteMessageNew)(MojoHandle message_pipe_handle,
                                 MojoMessageHandle message,