Sandbox the component updater's patcher utility process.

courgette/courgette.h

Index: courgette/courgette.h
diff --git a/courgette/courgette.h b/courgette/courgette.h
index 5f3dbb8367a81ba5f86f85ccd92399a3f7d7e9ac..29cf3c5749871b6069a2f85908989283862818ad 100644
--- a/courgette/courgette.h
+++ b/courgette/courgette.h
@@ -7,6 +7,7 @@
 
 #include <stddef.h>   // Required to define size_t on GCC
 
+#include "base/files/file.h"
 #include "base/files/file_path.h"
 
 namespace courgette {
@@ -74,6 +75,15 @@ class EncodedProgram;
 Status ApplyEnsemblePatch(SourceStream* old, SourceStream* patch,
                           SinkStream* output);
 
+// Applies the patch in |patch_file| to the bytes in |old_file| and writes the
+// transformed ensemble to |new_file|.
+// Returns C_OK unless something went wrong.
+// This function first validates that the patch file has a proper header, so the
+// function can be used to 'try' a patch.
+Status ApplyEnsemblePatch(base::File old_file,
+                          base::File patch_file,
+                          base::File new_file);
+
 // Applies the patch in |patch_file_name| to the bytes in |old_file_name| and
 // writes the transformed ensemble to |new_file_name|.
 // Returns C_OK unless something went wrong.