Port ChromeSyncShell build rules to GN

sync/BUILD.gn

Index: sync/BUILD.gn
diff --git a/sync/BUILD.gn b/sync/BUILD.gn
index b6a76afcacdaedbd367a88e1a780d74c510b44c3..c6fd22b821e71c8b680caaabc9ac1a1812926277 100644
--- a/sync/BUILD.gn
+++ b/sync/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
+import("//sync/protocol/protocol_sources.gni")
 import("//testing/test.gni")
 
 component("sync") {
@@ -841,6 +842,30 @@ if (is_android) {
     ]
   }
 
+  _test_support_sync_prepared_protos_dir =
+      "$root_gen_dir/test_support_sync_proto_java_prepare/"
+  action("test_support_sync_proto_java_prepare") {
+    script = "//sync/protocol/prepare_protos_for_java_tests.py"
+    inputs = sync_protocol_sources
+    outputs = process_file_template(
+            sync_protocol_sources,
+            [ "$_test_support_sync_prepared_protos_dir/{{source_file_part}}" ])
+    args = [
+      "--output_dir",
+      rebase_path(_test_support_sync_prepared_protos_dir, root_build_dir),
+    ]
+    args += rebase_path(sync_protocol_sources, root_build_dir)
+  }
+
+  # GYP: //sync/sync_tests.gypi:test_support_sync_proto_java
+  proto_java_library("test_support_sync_proto_java") {
+    proto_path = _test_support_sync_prepared_protos_dir
+    sources = get_target_outputs(":test_support_sync_proto_java_prepare")
+    deps = [
+      ":test_support_sync_proto_java_prepare",
+    ]
+  }
+
   # GYP: //sync/sync_tests.gypi:sync_java_test_support
   android_library("sync_java_test_support") {
     testonly = true