Create a FakeTetherService, which stubs out TetherService for development.

chrome/browser/chromeos/tether/fake_tether_service.cc

Index: chrome/browser/chromeos/tether/fake_tether_service.cc
diff --git a/chrome/browser/chromeos/tether/fake_tether_service.cc b/chrome/browser/chromeos/tether/fake_tether_service.cc
new file mode 100644
index 0000000000000000000000000000000000000000..5fe6bc89084f19c338d61f8a607908c9667d2418
--- /dev/null
+++ b/chrome/browser/chromeos/tether/fake_tether_service.cc
@@ -0,0 +1,46 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/chromeos/tether/fake_tether_service.h"
+
+constexpr char kTetherGuidPrefix[] = "tether-guid-";
+constexpr char kTetherNamePrefix[] = "tether";
+constexpr char kCarrier[] = "FakeCarrier";
+
+FakeTetherService::FakeTetherService(
+    Profile* profile,
+    chromeos::PowerManagerClient* power_manager_client,
+    chromeos::SessionManagerClient* session_manager_client,
+    cryptauth::CryptAuthService* cryptauth_service,
+    chromeos::NetworkStateHandler* network_state_handler)
+    : TetherService(profile,
+                    power_manager_client,
+                    session_manager_client,
+                    cryptauth_service,
+                    network_state_handler) {}
+
+void FakeTetherService::StartTetherIfEnabled() {
+  if (GetTetherTechnologyState() !=
+      chromeos::NetworkStateHandler::TechnologyState::TECHNOLOGY_ENABLED) {
+    return;
+  }
+
+  for (int i = 0; i < num_tether_networks_; ++i) {
+    network_state_handler()->AddTetherNetworkState(
+        kTetherGuidPrefix + std::to_string(i),
+        kTetherNamePrefix + std::to_string(i), kCarrier,
+        100 /* battery_percentage */, 100 /* signal_strength */,
+        false /* has_connected_to_host */);
+  }
+}
+
+void FakeTetherService::StopTether() {
+  for (int i = 0; i < num_tether_networks_; ++i) {
+    network_state_handler()->RemoveTetherNetworkState(kTetherGuidPrefix + i);
+  }
+}
+
+bool FakeTetherService::HasSyncedTetherHosts() const {
+  return true;
+}