Work around linker error of multiple definitions of pp::BlockUntilComplete

ppapi/cpp/completion_callback.h

 // Copyright (c) 2012 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 PPAPI_CPP_COMPLETION_CALLBACK_H_
 #define PPAPI_CPP_COMPLETION_CALLBACK_H_
 
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/cpp/logging.h"
@@ skipping 237 matching lines @@
  private:
   OutputStorageType* output_;
 };
 
 /// BlockUntilComplete() is used in place of an actual completion callback
 /// to request blocking behavior. If specified, the calling thread will block
 /// until the function completes. Blocking completion callbacks are only
 /// allowed from background threads.
 ///
 /// @return A <code>CompletionCallback</code> corresponding to a NULL callback.
-CompletionCallback BlockUntilComplete();
+inline CompletionCallback BlockUntilComplete() {
+  // Note: Explicitly inlined to avoid link errors when included into
+  // ppapi_proxy and ppapi_cpp_objects.
+  return CompletionCallback();
+}
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_COMPLETION_CALLBACK_H_