fix spelling of comments

remoting/base/tracer.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Tracer objects uresed to record an annotated timeline of events for use in
 // gathering performance data.  It wraps a TraceBuffer which is the raw data
 // for a trace. Tracer is threadsafe.
 //
 // TraceContext is a singleton that is used to give information for the current
 // trace. Clients should query TraceContext to find the current tracer and then
@@ skipping 97 matching lines @@
 
   void PopTracerInternal();
 
   Tracer* GetTracerInternal();
 
   std::vector<scoped_refptr<Tracer> > tracers_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceContext);
 };
 
-// Used to create a new tracer that NewRunnableMethod can propogate from.
+// Used to create a new tracer that NewRunnableMethod can propagate from.
 //
 // Declare this at the logical start of a "trace."  Calls to NewTracedMethod
 // that are done with the ScopedTracer object is alive will take a reference
 // to this tracer.  When such a method is invoked, it will push the trace back
 // onto the top of the TraceContext stack.  The result is that all asynchronous
 // tasks that are part of one logical flow will share the same trace.
 class ScopedTracer {
  public:
   ScopedTracer(const std::string& name) {
 #if defined(USE_TRACE)
@@ skipping 114 matching lines @@
                                                                   e, f, g));
 }
 
 #else
 #  define NewTracedMethod NewRunnableMethod
 #endif
 
 }  // namespace remoting
 
 #endif  // REMOTING_BASE_TRACER_H_