cc: Make property trees support external viewports

This makes the clip tree get updated for changes to the viewport
rect that happen on the compositor thread via calls to
LTHI::SetExternalDrawConstraints (this is used by Android WebView).

BUG=524106
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1413743005

Cr-Commit-Position: refs/heads/master@{#355278}

4 files changed, 39 insertions, 2 deletions

diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index 143c7b1..ccffb0f 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -2708,6 +2708,9 @@ void CalculateDrawPropertiesAndVerify(
             inputs->property_trees, inputs->page_scale_layer,
             inputs->page_scale_factor, inputs->device_scale_factor,
             inputs->device_transform);
+        // Similarly, the device viewport is shared between both trees.
+        inputs->property_trees->clip_tree.SetViewportClip(
+            gfx::RectF(gfx::SizeF(inputs->device_viewport_size)));
         ComputeVisibleRectsUsingPropertyTrees(
             inputs->root_layer, inputs->property_trees,
             inputs->can_render_to_separate_surface, &update_layer_list);
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 98118cc..2613af2 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2302,8 +2302,6 @@ void LayerTreeHostImpl::SetViewportSize(const gfx::Size& device_viewport_size) {
   client_->OnCanDrawStateChanged(CanDraw());
   SetFullRootLayerDamage();
   active_tree_->set_needs_update_draw_properties();
-  active_tree_->property_trees()->clip_tree.SetViewportClip(
-      gfx::RectF(gfx::SizeF(device_viewport_size)));
 }
 
 const gfx::Rect LayerTreeHostImpl::ViewportRectForTilePriority() const {
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 3824186..2eae9ac 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -8245,6 +8245,41 @@ TEST_F(LayerTreeHostImplTest, ExternalTransformSetNeedsRedraw) {
   }
 }
 
+TEST_F(LayerTreeHostImplTest, ExternalViewportAffectsVisibleRects) {
+  const gfx::Size layer_size(100, 100);
+  SetupScrollAndContentsLayers(layer_size);
+  LayerImpl* content_layer =
+      host_impl_->active_tree()->OuterViewportScrollLayer()->children()[0];
+  RebuildPropertyTrees();
+
+  bool update_lcd_text = false;
+
+  host_impl_->SetViewportSize(gfx::Size(90, 90));
+  host_impl_->active_tree()->UpdateDrawProperties(update_lcd_text);
+  EXPECT_EQ(gfx::Rect(90, 90), content_layer->visible_layer_rect());
+
+  gfx::Transform external_transform;
+  gfx::Rect external_viewport(10, 20);
+  gfx::Rect external_clip(layer_size);
+  bool resourceless_software_draw = false;
+  host_impl_->SetExternalDrawConstraints(
+      external_transform, external_viewport, external_clip, external_viewport,
+      external_transform, resourceless_software_draw);
+
+  // Visible rects should now be clipped by the external viewport.
+  host_impl_->active_tree()->UpdateDrawProperties(update_lcd_text);
+  EXPECT_EQ(gfx::Rect(10, 20), content_layer->visible_layer_rect());
+
+  // Clear the external viewport.
+  external_viewport = gfx::Rect();
+  host_impl_->SetExternalDrawConstraints(
+      external_transform, external_viewport, external_clip, external_viewport,
+      external_transform, resourceless_software_draw);
+
+  host_impl_->active_tree()->UpdateDrawProperties(update_lcd_text);
+  EXPECT_EQ(gfx::Rect(90, 90), content_layer->visible_layer_rect());
+}
+
 TEST_F(LayerTreeHostImplTest, ScrollAnimated) {
   SetupScrollAndContentsLayers(gfx::Size(100, 200));
 
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index 1207b40..262a52c 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -544,6 +544,7 @@ void BuildPropertyTreesTopLevelInternal(
     UpdatePageScaleFactorInPropertyTrees(property_trees, page_scale_layer,
                                          page_scale_factor, device_scale_factor,
                                          device_transform);
+    property_trees->clip_tree.SetViewportClip(gfx::RectF(viewport));
     return;
   }