cc: Update scroll offset before property tree scrolling and animation.

cc/trees/tree_synchronizer_unittest.cc

Index: cc/trees/tree_synchronizer_unittest.cc
diff --git a/cc/trees/tree_synchronizer_unittest.cc b/cc/trees/tree_synchronizer_unittest.cc
index f656634636a169d33a73916a3c430a072cc037ee..af086d62aab4973d29b425b5d11ba5129cdbd0f9 100644
--- a/cc/trees/tree_synchronizer_unittest.cc
+++ b/cc/trees/tree_synchronizer_unittest.cc
@@ -26,6 +26,7 @@
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/single_thread_proxy.h"
 #include "cc/trees/task_runner_provider.h"
+#include "cc/trees/transform_node.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cc {
@@ -620,6 +621,66 @@ TEST_F(TreeSynchronizerTest, SynchronizeScrollTreeScrollOffsetMap) {
   EXPECT_TRUE(is_equal(scroll_offset_map, scroll_tree.scroll_offset_map()));
 }
 
+TEST_F(TreeSynchronizerTest,
+       SynchronizeScrollTreeScrollOffsetMapFromMainToActive) {
+  host_->InitializeSingleThreaded(&single_thread_client_,
+                                  base::ThreadTaskRunnerHandle::Get());
+  FakeLayerTreeHostImpl* host_impl = host_->host_impl();
+
+  scoped_refptr<Layer> layer_tree_root = Layer::Create();
+  scoped_refptr<Layer> scroll_clip_layer = Layer::Create();
+  scoped_refptr<Layer> scroll_layer = Layer::Create();
+
+  layer_tree_root->AddChild(scroll_clip_layer);
+  scroll_clip_layer->AddChild(scroll_layer);
+
+  scroll_layer->SetScrollClipLayerId(scroll_clip_layer->id());
+  scroll_layer->SetScrollOffset(gfx::ScrollOffset(10, 20));
+
+  host_->SetRootLayer(layer_tree_root);
+  host_->BuildPropertyTreesForTesting();
+  host_->FinishCommitOnImplThread(host_impl);
+
+  ExpectTreesAreIdentical(layer_tree_root.get(),
+                          host_impl->active_tree()->root_layer_for_testing(),
+                          host_impl->active_tree());
+
+  // After the initial commit, scroll_offset_map in scroll_tree is expected to
+  // have one entry for scroll_layer and one entry for transient_scroll_layer,
+  // the pending base and active base must be the same at this stage.
+  ScrollTree::ScrollOffsetMap scroll_offset_map;
+  scroll_offset_map[scroll_layer->id()] = new SyncedScrollOffset;
+  scroll_offset_map[scroll_layer->id()]->PushFromMainThread(
+      scroll_layer->scroll_offset());
+  scroll_offset_map[scroll_layer->id()]->PushPendingToActive();
+  EXPECT_TRUE(
+      is_equal(scroll_offset_map, host_impl->active_tree()
+                                      ->property_trees()
+                                      ->scroll_tree.scroll_offset_map()));
+
+  // When running Layout tests in single thread mode, it is possible that the
+  // scroll tree's scroll offset map got cleared between commits, as a new test
+  // is started after finishing the previous one.
+  host_->property_trees()->scroll_tree.scroll_offset_map().clear();
+  scroll_layer->SetScrollOffset(gfx::ScrollOffset(0, 0));
+
+  host_->BuildPropertyTreesForTesting();
+  host_->FinishCommitOnImplThread(host_impl);
+
+  scroll_offset_map[scroll_layer->id()]->PushFromMainThread(
+      gfx::ScrollOffset(0, 0));
+  scroll_offset_map[scroll_layer->id()]->PushPendingToActive();
+  EXPECT_TRUE(
+      is_equal(scroll_offset_map, host_impl->active_tree()
+                                      ->property_trees()
+                                      ->scroll_tree.scroll_offset_map()));
+  EXPECT_EQ(host_impl->active_tree()
+                ->property_trees()
+                ->transform_tree.Node(scroll_layer->transform_tree_index())
+                ->scroll_offset,
+            gfx::ScrollOffset(0, 0));
+}
+
 TEST_F(TreeSynchronizerTest, RefreshPropertyTreesCachedData) {
   host_->InitializeSingleThreaded(&single_thread_client_,
                                   base::ThreadTaskRunnerHandle::Get());