Look up executable on PATH when given environment variables.

runtime/bin/process_linux.cc

Index: runtime/bin/process_linux.cc
diff --git a/runtime/bin/process_linux.cc b/runtime/bin/process_linux.cc
index bfaf4d4bf4aa933b05b40a4a8b90105f5c3b7782..8534dd9ed63dbe1e12b5ed549e7a9bf63539fbf5 100644
--- a/runtime/bin/process_linux.cc
+++ b/runtime/bin/process_linux.cc
@@ -17,6 +17,7 @@
 #include "bin/fdutils.h"
 #include "bin/thread.h"
 
+extern char **environ;
 
 // ProcessInfo is used to map a process id to the file descriptor for
 // the pipe used to communicate the exit code of the process to Dart.
@@ -461,15 +462,15 @@ int Process::Start(const char* path,
       ReportChildError(exec_control[1]);
     }
 
-    if (environment != NULL) {
-      TEMP_FAILURE_RETRY(
-          execve(path,
-                 const_cast<char* const*>(program_arguments),
-                 program_environment));
-    } else {
-      TEMP_FAILURE_RETRY(
-          execvp(path, const_cast<char* const*>(program_arguments)));
+    char **orig_environ = environ;

[Mads Ager (google), 2012/10/26 08:43:44]

char** orig_environ

However, I don't think there is a reason to save the old environment. We are in
the child process and if exec fails we are going to exit the child anyway and it
doesn't matter if we reset it.

[Bob Nystrom, 2012/10/30 18:16:59]

Removed.

[ahe, 2012/10/31 06:59:17]

I don't understand your reasoning.

ReportChildError calls strerror before exiting the process. strerror is affected
by locale (which is controlled by environment variables). Although there is no
call to setlocale, there is no way to know how error reporting code is going to
evolve.

+    if (program_environment != NULL) {
+      environ = program_environment;
     }
+    TEMP_FAILURE_RETRY(
+        execvp(path, const_cast<char* const*>(program_arguments)));
+    // Dead code, unless execvp fails.

[Mads Ager (google), 2012/10/26 08:43:44]

I think we can remove this. It doesn't matter, does it?

[Bob Nystrom, 2012/10/30 18:16:59]

I don't think so? Done.

+    environ = orig_environ;
+
     ReportChildError(exec_control[1]);
   }