sync: Add pre-commit update avoidance mode + flag

sync/tools/testserver/sync_testserver.py

Index: sync/tools/testserver/sync_testserver.py
diff --git a/sync/tools/testserver/sync_testserver.py b/sync/tools/testserver/sync_testserver.py
index 4fbfdaf9ac44af2a825e6c6735b7d57a06b12b96..53532cb5b7d57a6534958ca3c1b20cbcf9cc738a 100755
--- a/sync/tools/testserver/sync_testserver.py
+++ b/sync/tools/testserver/sync_testserver.py
@@ -150,7 +150,8 @@ class SyncPageHandler(testserver_base.BasePageHandler):
                     self.ChromiumSyncCreateSyncedBookmarksOpHandler,
                     self.ChromiumSyncEnableKeystoreEncryptionOpHandler,
                     self.ChromiumSyncRotateKeystoreKeysOpHandler,
-                    self.ChromiumSyncEnableManagedUserAcknowledgementHandler]
+                    self.ChromiumSyncEnableManagedUserAcknowledgementHandler,
+                    self.ChromiumSyncEnablePreCommitGetUpdateAvoidanceHandler]
 
     post_handlers = [self.ChromiumSyncCommandHandler,
                      self.ChromiumSyncTimeHandler]
@@ -427,6 +428,19 @@ class SyncPageHandler(testserver_base.BasePageHandler):
     self.wfile.write(raw_reply)
     return True
 
+  def ChromiumSyncEnablePreCommitGetUpdateAvoidanceHandler(self):
+    test_name = "/chromiumsync/enableprecommitgetupdateavoidance"
+    if not self._ShouldHandleRequest(test_name):
+      return False
+    result, raw_reply = (
+        self.server._sync_handler.HandleEnablePreCommitGetUpdateAvoidance())
+    self.send_response(result)
+    self.send_header('Content-Type', 'text/html')
+    self.send_header('Content-Length', len(raw_reply))
+    self.end_headers()
+    self.wfile.write(raw_reply)
+    return True
+
 class SyncServerRunner(testserver_base.TestServerRunner):
   """TestServerRunner for the net test servers."""