Spellling mistakes.

src/platform.h

Index: src/platform.h
===================================================================
--- src/platform.h	(revision 10399)
+++ src/platform.h	(working copy)
@@ -553,7 +553,7 @@
   virtual void Wait() = 0;
 
   // Suspends the calling thread until the counter is non zero or the timeout
-  // time has passsed. If timeout happens the return value is false and the
+  // time has passed. If timeout happens the return value is false and the
   // counter is unchanged. Otherwise the semaphore counter is decremented and
   // true is returned. The timeout value is specified in microseconds.
   virtual bool Wait(int timeout) = 0;