init: use Result<T> for builtin functions

We currently throw out the return values from builtin functions and
occasionally log errors with no supporting context.  This change uses
the newly introduced Result<T> class to communicate a successful result
or an error back to callers in order to print an error with clear
context when a builtin fails.

Example:

init: Command 'write /sys/class/leds/vibrator/trigger transient' action=init (/init.rc:245) took 0ms and failed: Unable to write to file '/sys/class/leds/vibrator/trigger': open() failed: No such file or directory

Test: boot bullhead
Merged-In: Idc18f331d2d646629c6093c1e0f2996cf9b42aec
Change-Id: Idc18f331d2d646629c6093c1e0f2996cf9b42aec
diff --git a/init/bootchart.h b/init/bootchart.h
index e4f7b59..f614f71 100644
--- a/init/bootchart.h
+++ b/init/bootchart.h
@@ -20,10 +20,12 @@
 #include <string>
 #include <vector>
 
+#include "result.h"
+
 namespace android {
 namespace init {
 
-int do_bootchart(const std::vector<std::string>& args);
+Result<Success> do_bootchart(const std::vector<std::string>& args);
 
 }  // namespace init
 }  // namespace android