Trigger windowinfo updates when alpha changes

Input and TrustedPresentationListener logic relies on layer alpha. This change ensures
that SurfaceFlinger sends the updated window info when only the alpha changes.

Fixes: 325254898
Test: presubmit
Flag: EXEMPT bugfix
Change-Id: I6b9a5b2874add278245cb682c5362c18403c70b0
diff --git a/services/surfaceflinger/tests/unittests/LayerSnapshotTest.cpp b/services/surfaceflinger/tests/unittests/LayerSnapshotTest.cpp
index bd0accd..8cf3f03 100644
--- a/services/surfaceflinger/tests/unittests/LayerSnapshotTest.cpp
+++ b/services/surfaceflinger/tests/unittests/LayerSnapshotTest.cpp
@@ -1161,6 +1161,16 @@
             gui::WindowInfo::InputConfig::TRUSTED_OVERLAY));
 }
 
+TEST_F(LayerSnapshotTest, alphaChangesPropagateToInput) {
+    Region touch{Rect{0, 0, 1000, 1000}};
+    setTouchableRegion(1, touch);
+    UPDATE_AND_VERIFY(mSnapshotBuilder, STARTING_ZORDER);
+
+    setAlpha(1, 0.5f);
+    UPDATE_AND_VERIFY(mSnapshotBuilder, STARTING_ZORDER);
+    EXPECT_EQ(getSnapshot(1)->inputInfo.alpha, 0.5f);
+}
+
 TEST_F(LayerSnapshotTest, isFrontBuffered) {
     setBuffer(1,
               std::make_shared<renderengine::mock::FakeExternalTexture>(