Support passing an environment variable map to child processes.

runtime/bin/process.h

Index: runtime/bin/process.h
diff --git a/runtime/bin/process.h b/runtime/bin/process.h
index 0916c07c558e57460d9046153ba6258dc9f7a2d8..a23551a4534c428ff9ace42353ccdb7d445cc734 100644
--- a/runtime/bin/process.h
+++ b/runtime/bin/process.h
@@ -17,6 +17,8 @@ class Process {
                    char* arguments[],
                    intptr_t arguments_length,
                    const char* working_directory,
+                   char* environment[],
+                   intptr_t environment_length,
                    intptr_t* in,
                    intptr_t* out,
                    intptr_t* err,