Don't fork dex2oat process on target device.

Change-Id: I35370d328aaa1aaaed5b56e62e51c4c74afa9cba
diff --git a/src/elf_image.h b/src/elf_image.h
index 79bd84e..79bfd90 100644
--- a/src/elf_image.h
+++ b/src/elf_image.h
@@ -18,6 +18,7 @@
 #define ART_SRC_ELF_IMAGE_H_
 
 #include "globals.h"
+#include <string>
 #include <vector>
 
 namespace art {
@@ -28,6 +29,10 @@
       : begin_(&*v.begin()), size_(v.size()) {
   }
 
+  explicit ElfImage(const std::string& s)
+      : begin_(reinterpret_cast<const uint8_t*>(s.data())), size_(s.size()) {
+  }
+
   explicit ElfImage(const byte* begin, size_t size)
       : begin_(begin), size_(size) {
   }