[BGPT] Add fast border radius support behind a flag

"Fast border radius" means using a procedural GL shader to
draw rounded corners, not a mask layer.

Bug: 947715

Change-Id: I51503223d4b4291cea0496fc44ecd72888af6710
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1566727Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#650563}

third_party/blink/renderer/platform/graphics/compositing/paint_artifact_compositor.cc

@@ -1036,6 +1036,8 @@ static bool IsRenderSurfaceCandidate(
       blink_effects[effect.id] &&
       blink_effects[effect.id]->HasActiveOpacityAnimation())
     return true;
+  if (effect.is_fast_rounded_corner)
+    return true;
   return false;
 }
 

third_party/blink/renderer/platform/graphics/compositing/property_tree_manager.cc

@@ -504,6 +504,9 @@ int PropertyTreeManager::EnsureCompositorScrollNode(
 }
 
 void PropertyTreeManager::EmitClipMaskLayer() {
+  if (RuntimeEnabledFeatures::FastBorderRadiusEnabled())
+    return;
+
   cc::EffectNode& mask_isolation = *GetEffectTree().Node(current_.effect_id);
   if (pending_synthetic_mask_layers_.Contains(mask_isolation.id))
     return;
@@ -755,8 +758,15 @@ SkBlendMode PropertyTreeManager::SynthesizeCcEffectsForClipsIfNeeded(
     const auto& transform = pending_clip.clip->LocalTransformSpace();
     synthetic_effect.transform_id = EnsureCompositorTransformNode(transform);
     synthetic_effect.double_sided = !transform.IsBackfaceHidden();
-    synthetic_effect.has_render_surface = true;
-    pending_synthetic_mask_layers_.insert(synthetic_effect.id);
+
+    if (RuntimeEnabledFeatures::FastBorderRadiusEnabled()) {
+      synthetic_effect.rounded_corner_bounds =
+          gfx::RRectF(pending_clip.clip->ClipRect());
+      synthetic_effect.is_fast_rounded_corner = true;
+    } else {
+      synthetic_effect.has_render_surface = true;
+      pending_synthetic_mask_layers_.insert(synthetic_effect.id);
+    }
 
     // Clip and kDstIn do not commute. This shall never be reached because
     // kDstIn is only used internally to implement CSS clip-path and mask,

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -524,6 +524,9 @@
     {
       name: "FallbackCursorMode",
     },
+    {
+      name: "FastBorderRadius",
+    },
     {
       name: "FastFlatTreeTraversal",
       status: "stable",