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 38ac6836b0c07bca0d222d46e0759ee90c40c98d..f9108b4c7c92af3687ae3e33f26757556a2aa88b 100644
--- a/ppapi/proxy/file_io_resource.h
+++ b/ppapi/proxy/file_io_resource.h
@@ -68,7 +68,6 @@ 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
@@ -101,7 +100,11 @@ 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: