Expose ability to download network service impl in SDK.

mojo/tools/roll/roll_network_service.py

Index: mojo/tools/roll/roll_network_service.py
diff --git a/mojo/tools/roll/roll_network_service.py b/mojo/tools/roll/roll_network_service.py
index 12122ba11aebd2513bda7ae260c83ab84f8c47c2..2cdf31544cdc3d2c4587dfb4faecfa1aaa170ef0 100755
--- a/mojo/tools/roll/roll_network_service.py
+++ b/mojo/tools/roll/roll_network_service.py
@@ -33,7 +33,9 @@ def roll(target_version):
   network_service_path = os.path.join(
       mojo_root_dir, "mojo", "services", "network")
   mojoms_path = os.path.join(network_service_path, "public", "interfaces")
-  version_path = os.path.join(network_service_path, "VERSION")
+  mojo_public_tools_path = os.path.join(
+      mojo_root_dir, "mojo", "public", "tools")
+  version_path = os.path.join(mojo_public_tools_path, "NETWORK_SERVICE_VERSION")
 
   try:
     with tempfile.NamedTemporaryFile() as temp_zip_file:
@@ -59,7 +61,7 @@ def roll(target_version):
     stamp_file.write(target_version)
 
   system(["git", "add", "public"], cwd=network_service_path)
-  system(["git", "add", "VERSION"], cwd=network_service_path)
+  system(["git", "add", "NETWORK_SERVICE_VERSION"], cwd=mojo_public_tools_path)
   commit("Roll the network service to https://crrev.com/" + chromium_rev,
          cwd=mojo_root_dir)
   return 0