Make Platform.executable return a fully qualified path the the executable

runtime/bin/platform_macos.cc

Index: runtime/bin/platform_macos.cc
diff --git a/runtime/bin/platform_macos.cc b/runtime/bin/platform_macos.cc
index 55ccd213f87b3e7ec1ea6b3192112cbea22c803c..702bf017806e811b78243ca729276b7c8cdc8872 100644
--- a/runtime/bin/platform_macos.cc
+++ b/runtime/bin/platform_macos.cc
@@ -5,6 +5,8 @@
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
+#include <mach-o/dyld.h>
+
 #include "bin/platform.h"
 
 #include <crt_externs.h>  // NOLINT
@@ -75,6 +77,23 @@ void Platform::FreeEnvironment(char** env, intptr_t count) {
   delete[] env;
 }
 
+
+char* Platform::ResolveExecutablePath() {
+  // Get the required length of the buffer.
+  uint32_t path_size = 0;
+  char* path = NULL;
+  if (_NSGetExecutablePath(path, &path_size) == 0) {
+    return NULL;
+  }
+  // Allocate buffer and get executable path.
+  path = reinterpret_cast<char*>(malloc(path_size));
+  if (_NSGetExecutablePath(path, &path_size) != 0) {
+    free(path);
+    return NULL;
+  }
+  return path;
+}
+
 }  // namespace bin
 }  // namespace dart