Implement or remove some process LaunchOptions under Fuchsia.

- Implement LaunchOptions::wait.
- Move |maximize_relimits| to exist conditional on OS_LINUX.
- Don't define |real_path| or |pre_exec_delegate| under Fuchsia.

Bug: 799268
Change-Id: I4ec2643fc16a72f99518e892e353be72e6329130
Reviewed-on: https://chromium-review.googlesource.com/852981
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528031}

CrOS-Libchrome-Original-Commit: c6b685d005b61d767406ed41dc963e0a5cd8e327
diff --git a/base/process/launch.h b/base/process/launch.h
index a6ed7fb..caa05c4 100644
--- a/base/process/launch.h
+++ b/base/process/launch.h
@@ -200,7 +200,7 @@
       LP_CLONE_FDIO_NAMESPACE | LP_CLONE_DEFAULT_JOB | LP_CLONE_FDIO_STDIO;
 #endif  // defined(OS_FUCHSIA)
 
-#if defined(OS_POSIX)
+#if defined(OS_POSIX) && !defined(OS_FUCHSIA)
   // If not empty, launch the specified executable instead of
   // cmdline.GetProgram(). This is useful when it is necessary to pass a custom
   // argv[0].
@@ -223,7 +223,7 @@
   // inheriting the parent's process group.  The pgid of the child process
   // will be the same as its pid.
   bool new_process_group = false;
-#endif  // defined(OS_POSIX)
+#endif  // defined(OS_POSIX) && !defined(OS_FUCHSIA)
 
 #if defined(OS_CHROMEOS)
   // If non-negative, the specified file descriptor will be set as the launched