4 files changed, 63 insertions, 9 deletions

diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 1f8e5a8..763f05e 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -936,7 +936,10 @@ bool PictureLayerImpl::MarkVisibleTilesAsRequired(
     if (optional_twin_tiling) {
       Tile* twin_tile = optional_twin_tiling->TileAt(iter.i(), iter.j());
       if (!twin_tile || twin_tile == tile) {
-        twin_had_missing_tile = true;
+        // However if the shared tile is being used on the active tree, then
+        // there's no missing content in this place, and low res is not needed.
+        if (!twin_tile || !twin_tile->IsReadyToDraw())
+          twin_had_missing_tile = true;
         continue;
       }
     }
diff --git a/cc/layers/picture_layer_impl_unittest.cc b/cc/layers/picture_layer_impl_unittest.cc
index 249dcf0..ba6c6bb 100644
--- a/cc/layers/picture_layer_impl_unittest.cc
+++ b/cc/layers/picture_layer_impl_unittest.cc
@@ -2822,7 +2822,7 @@ TEST_F(PictureLayerImplTest, LowResReadyToDrawNotEnoughToActivate) {
   EXPECT_TRUE(pending_layer_->AllTilesRequiredForActivationAreReadyToDraw());
 }
 
-TEST_F(PictureLayerImplTest, HighResReadyToDrawNotEnoughToActivate) {
+TEST_F(PictureLayerImplTest, HighResReadyToDrawEnoughToActivate) {
   gfx::Size tile_size(100, 100);
   gfx::Size layer_bounds(1000, 1000);
 
@@ -2841,12 +2841,58 @@ TEST_F(PictureLayerImplTest, HighResReadyToDrawNotEnoughToActivate) {
   // Initialize all high-res tiles.
   pending_layer_->SetAllTilesReadyInTiling(pending_layer_->HighResTiling());
 
-  // High-res tiles should not be enough.
+  // High-res tiles should be enough, since they cover everything visible.
+  EXPECT_TRUE(pending_layer_->AllTilesRequiredForActivationAreReadyToDraw());
+}
+
+TEST_F(PictureLayerImplTest,
+       SharedActiveHighResReadyAndPendingLowResReadyNotEnoughToActivate) {
+  gfx::Size tile_size(100, 100);
+  gfx::Size layer_bounds(1000, 1000);
+
+  SetupDefaultTreesWithFixedTileSize(layer_bounds, tile_size);
+
+  // Make sure some tiles are not shared.
+  pending_layer_->set_invalidation(gfx::Rect(gfx::Point(50, 50), tile_size));
+
+  CreateHighLowResAndSetAllTilesVisible();
+
+  // Initialize all high-res tiles in the active layer.
+  active_layer_->SetAllTilesReadyInTiling(active_layer_->HighResTiling());
+  // And all the low-res tiles in the pending layer.
+  pending_layer_->SetAllTilesReadyInTiling(pending_layer_->LowResTiling());
+
+  pending_layer_->MarkVisibleResourcesAsRequired();
+
+  // The unshared high-res tiles are not ready, so we cannot activate.
   EXPECT_FALSE(pending_layer_->AllTilesRequiredForActivationAreReadyToDraw());
 
-  // Initialize remaining tiles.
-  pending_layer_->SetAllTilesReady();
+  // When the unshared pending high-res tiles are ready, we can activate.
+  pending_layer_->SetAllTilesReadyInTiling(pending_layer_->HighResTiling());
+  EXPECT_TRUE(pending_layer_->AllTilesRequiredForActivationAreReadyToDraw());
+}
+
+TEST_F(PictureLayerImplTest, SharedActiveHighResReadyNotEnoughToActivate) {
+  gfx::Size tile_size(100, 100);
+  gfx::Size layer_bounds(1000, 1000);
+
+  SetupDefaultTreesWithFixedTileSize(layer_bounds, tile_size);
 
+  // Make sure some tiles are not shared.
+  pending_layer_->set_invalidation(gfx::Rect(gfx::Point(50, 50), tile_size));
+
+  CreateHighLowResAndSetAllTilesVisible();
+
+  // Initialize all high-res tiles in the active layer.
+  active_layer_->SetAllTilesReadyInTiling(active_layer_->HighResTiling());
+
+  pending_layer_->MarkVisibleResourcesAsRequired();
+
+  // The unshared high-res tiles are not ready, so we cannot activate.
+  EXPECT_FALSE(pending_layer_->AllTilesRequiredForActivationAreReadyToDraw());
+
+  // When the unshared pending high-res tiles are ready, we can activate.
+  pending_layer_->SetAllTilesReadyInTiling(pending_layer_->HighResTiling());
   EXPECT_TRUE(pending_layer_->AllTilesRequiredForActivationAreReadyToDraw());
 }
 
diff --git a/cc/test/fake_picture_layer_impl.cc b/cc/test/fake_picture_layer_impl.cc
index 78924cd..98e0f6e 100644
--- a/cc/test/fake_picture_layer_impl.cc
+++ b/cc/test/fake_picture_layer_impl.cc
@@ -140,13 +140,17 @@ void FakePictureLayerImpl::SetAllTilesReadyInTiling(
   std::vector<Tile*> tiles = tiling->AllTilesForTesting();
   for (size_t tile_idx = 0; tile_idx < tiles.size(); ++tile_idx) {
     Tile* tile = tiles[tile_idx];
-    ManagedTileState& state = tile->managed_state();
-    for (size_t mode_idx = 0; mode_idx < NUM_RASTER_MODES; ++mode_idx)
-      state.tile_versions[mode_idx].SetSolidColorForTesting(true);
-    DCHECK(tile->IsReadyToDraw());
+    SetTileReady(tile);
   }
 }
 
+void FakePictureLayerImpl::SetTileReady(Tile* tile) {
+  ManagedTileState& state = tile->managed_state();
+  for (size_t mode_idx = 0; mode_idx < NUM_RASTER_MODES; ++mode_idx)
+    state.tile_versions[mode_idx].SetSolidColorForTesting(true);
+  DCHECK(tile->IsReadyToDraw());
+}
+
 void FakePictureLayerImpl::CreateDefaultTilingsAndTiles() {
   layer_tree_impl()->UpdateDrawProperties();
 
diff --git a/cc/test/fake_picture_layer_impl.h b/cc/test/fake_picture_layer_impl.h
index 915b740..fbaecf7 100644
--- a/cc/test/fake_picture_layer_impl.h
+++ b/cc/test/fake_picture_layer_impl.h
@@ -108,6 +108,7 @@ class FakePictureLayerImpl : public PictureLayerImpl {
   void SetAllTilesVisible();
   void SetAllTilesReady();
   void SetAllTilesReadyInTiling(PictureLayerTiling* tiling);
+  void SetTileReady(Tile* tile);
   void ResetAllTilesPriorities();
   PictureLayerTilingSet* GetTilings() { return tilings_.get(); }