cc: Don't require low res to activate for shared ready-to-draw tiles.

When a tile is shared (no invalidation) and is being drawn on the
active tree (ready-to-draw), then that tile is not marked as required
for activation since activating it can't cause a bad-resolution flash.

However, we also would also say that "twin_had_missing_tile" in this
scenario, which causes us to mark low-res tilings as required. But
this is a bug since the tile is not missing in this case, and we do
not need low res to fill it in.

Instead, check to see if the active tree's tile is /not/ ready-to-draw.
When that is the case, the active tile is not being drawn and is
actually missing. Then a low res tile should be required if the
active tree is showing a low res tile in the same place.

For perf tests without scrolling (ie pages that just update in place
without input), this fixes us to never require low res tiles to
activate, since we won't show them.

R=enne, vmpstr
BUG=407121

Review URL: https://codereview.chromium.org/540663002

Cr-Commit-Position: refs/heads/master@{#293262}

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(); }