cc/blimp: Add synchronization for scroll/scale state.

cc/blimp/synced_property_remote_unittest.cc

+// Copyright 2016 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 "cc/blimp/synced_property_remote.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cc {
+namespace {
+
+TEST(SyncedPropertyRemoteTest, BasicDeltaTracking) {
+  SyncedPropertyRemote<ScaleGroup> synced_float;
+
+  // Set up the initial value.
+  float initial_state = 0.5f;
+  synced_float.PushFromEngineMainThread(initial_state);
+  EXPECT_EQ(synced_float.EngineMain(), initial_state);
+
+  // Apply a delta from the impl thread.
+  float delta_from_impl = 0.2f;
+  synced_float.UpdateDeltaFromImplThread(initial_state * delta_from_impl);
+  EXPECT_EQ(synced_float.DeltaNotAppliedOnEngine(), delta_from_impl);
+  EXPECT_EQ(synced_float.EngineMain(), initial_state);
+
+  // Pull a state update for the engine.
+  float delta_to_send = synced_float.PullDeltaForEngineUpdate();
+  EXPECT_EQ(delta_to_send, delta_from_impl);
+
+  // The initial delta should still be reported as unapplied.
+  EXPECT_EQ(synced_float.DeltaNotAppliedOnEngine(), delta_from_impl);
+
+  // Now send some more delta from impl. It should be included in the unapplied
+  // delta.
+  float second_delta_from_impl = 0.3f;
+  synced_float.UpdateDeltaFromImplThread(synced_float.EngineMain() *
+                                         second_delta_from_impl);
+  float third_delta_from_impl = 0.4f;
+  synced_float.UpdateDeltaFromImplThread(synced_float.EngineMain() *
+                                         third_delta_from_impl);
+
+  float expected_total_delta =
+      delta_from_impl * second_delta_from_impl * third_delta_from_impl;
+  EXPECT_EQ(synced_float.DeltaNotAppliedOnEngine(), expected_total_delta);
+
+  // Inform that the delta was applied on the engine and make sure it is
+  // pre-emptively applied on the client.
+  synced_float.DidApplySentDeltaOnEngine();
+  EXPECT_EQ(synced_float.EngineMain(), initial_state * delta_from_impl);
+
+  // Now pull another delta, it should be now the accumulated delta.
+  EXPECT_EQ(synced_float.PullDeltaForEngineUpdate(),
+            second_delta_from_impl * third_delta_from_impl);
+}
+
+}  // namespace
+}  // namespace cc