Relanding "Multiprocess test client: Android child process launcher rework."

base/process/process.h

Index: base/process/process.h
diff --git a/base/process/process.h b/base/process/process.h
index 5538475863b09f65cba4d7bede6db24b27091f4c..978ca78c04683dd4e0c87a388e9c10e8e77a2afd 100644
--- a/base/process/process.h
+++ b/base/process/process.h
@@ -108,12 +108,12 @@ class BASE_EXPORT Process {
   // any process.
   // NOTE: |exit_code| is optional, nullptr can be passed if the exit code is
   // not required.
-  bool WaitForExit(int* exit_code);
+  bool WaitForExit(int* exit_code) const;
 
   // Same as WaitForExit() but only waits for up to |timeout|.
   // NOTE: |exit_code| is optional, nullptr can be passed if the exit code
   // is not required.
-  bool WaitForExitWithTimeout(TimeDelta timeout, int* exit_code);
+  bool WaitForExitWithTimeout(TimeDelta timeout, int* exit_code) const;
 
 #if defined(OS_MACOSX)
   // The Mac needs a Mach port in order to manipulate a process's priority,