Proof-reading comments in base/message_loop/.

This CL contains a few minor changes to comments that I made while
skimming through the code. Mostly spelling changes.

Review URL: https://codereview.chromium.org/1255673004

Cr-Commit-Position: refs/heads/master@{#340383}


CrOS-Libchrome-Original-Commit: 15926f8886b8fa20c044c02eb0387f44e611c993
diff --git a/base/message_loop/message_loop.h b/base/message_loop/message_loop.h
index fbb8309..63a29f1 100644
--- a/base/message_loop/message_loop.h
+++ b/base/message_loop/message_loop.h
@@ -308,18 +308,18 @@
   void SetTaskRunner(scoped_refptr<SingleThreadTaskRunner> task_runner);
 
   // Enables or disables the recursive task processing. This happens in the case
-  // of recursive message loops. Some unwanted message loop may occurs when
+  // of recursive message loops. Some unwanted message loops may occur when
   // using common controls or printer functions. By default, recursive task
   // processing is disabled.
   //
-  // Please utilize |ScopedNestableTaskAllower| instead of calling these methods
-  // directly.  In general nestable message loops are to be avoided.  They are
+  // Please use |ScopedNestableTaskAllower| instead of calling these methods
+  // directly.  In general, nestable message loops are to be avoided.  They are
   // dangerous and difficult to get right, so please use with extreme caution.
   //
   // The specific case where tasks get queued is:
   // - The thread is running a message loop.
-  // - It receives a task #1 and execute it.
-  // - The task #1 implicitly start a message loop, like a MessageBox in the
+  // - It receives a task #1 and executes it.
+  // - The task #1 implicitly starts a message loop, like a MessageBox in the
   //   unit test. This can also be StartDoc or GetSaveFileName.
   // - The thread receives a task #2 before or while in this second message
   //   loop.
@@ -420,7 +420,7 @@
   // and then pass it to the thread where the message loop actually runs.
   // The message loop's BindToCurrentThread() method must be called on the
   // thread the message loop runs on, before calling Run().
-  // Before BindToCurrentThread() is called only Post*Task() functions can
+  // Before BindToCurrentThread() is called, only Post*Task() functions can
   // be called on the message loop.
   static scoped_ptr<MessageLoop> CreateUnbound(
       Type type,
@@ -511,7 +511,7 @@
   bool nestable_tasks_allowed_;
 
 #if defined(OS_WIN)
-  // Should be set to true before calling Windows APIs like TrackPopupMenu, etc
+  // Should be set to true before calling Windows APIs like TrackPopupMenu, etc.
   // which enter a modal message loop.
   bool os_modal_loop_;
 #endif