[PPAPI] Fix a bunch of spelling mistakes

ppapi/cpp/message_loop.h

Index: ppapi/cpp/message_loop.h
diff --git a/ppapi/cpp/message_loop.h b/ppapi/cpp/message_loop.h
index fa38c669ef66599dcba588ffca7dd75912f32f74..9e28b2d835b18b3d92786e78c7750b4545934446 100644
--- a/ppapi/cpp/message_loop.h
+++ b/ppapi/cpp/message_loop.h
@@ -24,7 +24,8 @@ class InstanceHandle;
 /// suddenly see their PP_Resource handles become invalid. In this case, calls
 /// will fail with PP_ERROR_BADRESOURCE. If you need to access data associated
 /// with your instance, you will probably want to create some kind of threadsafe
-/// proxy object that can handle asynchonous destruction of the instance object.
+/// proxy object that can handle asynchronous destruction of the instance
+/// object.
 ///
 /// Typical usage:
 ///   On the main thread:
@@ -37,7 +38,7 @@ class InstanceHandle;
 ///    - Call AttachToCurrentThread() with the message loop resource.
 ///    - Call Run() with the message loop resource.
 ///
-///   Your callacks should look like this:
+///   Your callbacks should look like this:
 ///      void DoMyWork(void* user_data, int32_t status) {
 ///        if (status != PP_OK) {
 ///          Cleanup();  // e.g. free user_data.
@@ -199,7 +200,7 @@ class MessageLoop : public Resource {
   /// @param callback A pointer to the completion callback to execute from the
   /// message loop.
   ///
-  /// @param delay_ms The number of millseconds to delay execution of the given
+  /// @param delay_ms The number of milliseconds to delay execution of the given
   /// completion callback. Passing 0 means it will get queued normally and
   /// executed in order.
   ///