Installd: Add error message to dexopt

To give better messages to the binder call, add an out parameter.
This is only the start, threading things further into the calls
dexopt makes, and formatting according to exit codes, will be in
a follow-up CL.

Test: installd_dexopt_test
Change-Id: I0271212c5cddf3a6317d6b597e97537865723fdc
diff --git a/cmds/installd/dexopt.h b/cmds/installd/dexopt.h
index 62f9467..bb6fab3 100644
--- a/cmds/installd/dexopt.h
+++ b/cmds/installd/dexopt.h
@@ -106,7 +106,7 @@
         int dexopt_needed, const char* oat_dir, int dexopt_flags, const char* compiler_filter,
         const char* volume_uuid, const char* class_loader_context, const char* se_info,
         bool downgrade, int target_sdk_version, const char* profile_name,
-        const char* dexMetadataPath, const char* compilation_reason);
+        const char* dexMetadataPath, const char* compilation_reason, std::string* error_msg);
 
 bool calculate_oat_file_path_default(char path[PKG_PATH_MAX], const char *oat_dir,
         const char *apk_path, const char *instruction_set);