PPAPI: Implement PPB_FileMapping on POSIX

ppapi/proxy/file_io_resource.h

Index: ppapi/proxy/file_io_resource.h
diff --git a/ppapi/proxy/file_io_resource.h b/ppapi/proxy/file_io_resource.h
index d6465fd48142736750ba9ff3b0068782f99c4a99..5d580350384ea09f5db4809856244f9219087142 100644
--- a/ppapi/proxy/file_io_resource.h
+++ b/ppapi/proxy/file_io_resource.h
@@ -69,7 +69,6 @@ class PPAPI_PROXY_EXPORT FileIOResource
       PP_FileHandle* handle,
       scoped_refptr<TrackedCallback> callback) OVERRIDE;
 
- private:
   // FileHandleHolder is used to guarantee that file operations will have a
   // valid FD to operate on, even if they're in a different thread.
   // If instead we just passed the raw FD, the FD could be closed before the
@@ -102,7 +101,11 @@ class PPAPI_PROXY_EXPORT FileIOResource
     ~FileHandleHolder();
     PP_FileHandle raw_handle_;
   };
+  scoped_refptr<FileHandleHolder> file_handle() {
+    return file_handle_;
+  }
 
+ private:
   // Class to perform file query operations across multiple threads.
   class QueryOp : public base::RefCountedThreadSafe<QueryOp> {
    public: