cc: nine patch: add occlusion support

ash/mus/shadow.cc

Index: ash/mus/shadow.cc
diff --git a/ash/mus/shadow.cc b/ash/mus/shadow.cc
index 9d6b7183292e86d7facaa2f3240ac5e58b64f459..c215c96a474b15366a6ec88ca7fb50594f0915eb 100644
--- a/ash/mus/shadow.cc
+++ b/ash/mus/shadow.cc
@@ -32,6 +32,10 @@ const int kActiveInteriorInset = 64;
 const int kInactiveInteriorInset = 64;
 const int kSmallInteriorInset = 4;
 
+// Rounded corners are overdrawn on top of the window's content layer,
+// we need to exclude them from the occlusion area.
+const int kRoundedCornerRadius = 2;
+
 // Duration for opacity animation in milliseconds.
 const int kShadowAnimationDurationMs = 100;
 
@@ -194,11 +198,23 @@ void Shadow::UpdateLayerBounds() {
   int aperture = GetShadowApertureForStyle(style_);
   int aperture_x = std::min(aperture, layer_bounds.width() / 2);
   int aperture_y = std::min(aperture, layer_bounds.height() / 2);
-  shadow_layer_->UpdateNinePatchLayerAperture(
-      gfx::Rect(aperture_x, aperture_y, image_size_.width() - aperture_x * 2,
-                image_size_.height() - aperture_y * 2));
+  gfx::Rect aperture_rect(aperture_x, aperture_y,
+                          image_size_.width() - aperture_x * 2,
+                          image_size_.height() - aperture_y * 2);
+
+  shadow_layer_->UpdateNinePatchLayerAperture(aperture_rect);
   shadow_layer_->UpdateNinePatchLayerBorder(
       gfx::Rect(aperture_x, aperture_y, aperture_x * 2, aperture_y * 2));
+
+  // The content bounds in the shadow's layer space are offsetted by
+  // |interior_inset_|. The occlusion area also has to be shrinked to
+  // allow rounded corners overdrawing on top of the window's content.
+  gfx::Rect content_bounds(
+      content_bounds_.x() + interior_inset_ + kRoundedCornerRadius,
+      content_bounds_.y() + interior_inset_ + kRoundedCornerRadius,
+      content_bounds_.width() - 2 * kRoundedCornerRadius,
+      content_bounds_.height() - 2 * kRoundedCornerRadius);
+  shadow_layer_->UpdateNinePatchOcclusion(content_bounds);
 }
 
 void Shadow::OnWindowDestroyed(::mus::Window* window) {