device_orientation::DispatcherHost: one Provider observer per render_view_id.

chrome/browser/device_orientation/provider.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.
 
 #ifndef CHROME_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_
 #define CHROME_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_
 
 #include "base/logging.h"
 #include "base/ref_counted.h"
 
@@ skipping 15 matching lines @@
   // The caller should store the returned pointer in a scoped_refptr.
   // The Provider instance is lazily constructed when GetInstance() is called,
   // and destructed when the last scoped_refptr referring to it is destructed.
   static Provider* GetInstance();
 
   // Inject a mock Provider for testing. Only a weak pointer to the injected
   // object will be held by Provider, i.e. it does not itself contribute to the
   // injected object's reference count.
   static void SetInstanceForTests(Provider* provider);
 
+  // Note: AddObserver may call back synchronously to the observer with
+  // orientation data.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
  protected:
   Provider() {}
   virtual ~Provider() {
     DCHECK(instance_ == this);
     instance_ = NULL;
   }
 
  private:
   friend class base::RefCountedThreadSafe<Provider>;
   static Provider* instance_;
 
   DISALLOW_COPY_AND_ASSIGN(Provider);
 };
 
 }  // namespace device_orientation
 
 #endif  // CHROME_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_