Revert "[Honeydew][ui] e2e tests should temporarily ignore pixel alpha values"

This reverts commit c061093.

Reason for revert: Ignoring pixel alpha values turns out to not be sufficient when comparing two screenshots with the same content but differing opacity. A more comprehensive solution is needed.

Original change's description:
> [Honeydew][ui] e2e tests should temporarily ignore pixel alpha values
>
> With the introduction of opacity-based brightness, e2e tests must ignore pixel alpha values to avoid failures caused by auto-brightness changing image opacity. Opacity-based brightness is only a temporary solution until the backlight driver becomes available, at which point we will revert this change back.
>
> Bug: b/397960210
> Change-Id: Ia230c7555068cc34156aabcede45c50807999a11
> Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1229144
> Reviewed-by: Jianpeng Chao <[email protected]>
> Commit-Queue: Auto-Submit <[email protected]>
> Fuchsia-Auto-Submit: Justin Kobler <[email protected]>

Bug: b/397960210
Change-Id: Id6127f86ccd910cf759f30e9ddd2b675d8f7379f
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1236286
Fuchsia-Auto-Submit: Justin Kobler <[email protected]>
Reviewed-by: Jianpeng Chao <[email protected]>
Reviewed-by: RubberStamper 🤖 <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>

Author: Justin Kobler

src/testing/end_to_end/honeydew/honeydew/affordances/ui/screenshot/tests/unit_tests/types_test.py

@@ -282,9 +282,7 @@ def test_pixel_similarity_different_sized_images(self) -> None:
             param(
                 pixels1=[WHITE, RED, TRANSPARENT, GREEN],
                 pixels2=[RED, WHITE, BLUE, BLACK],
-                # TODO(b/399391948): Temporarily expect 0.75 similarity while we ignore pixel alpha
-                # values. When we eventually revert this, expected_similarity will return to 0.5.
-                expected_similarity=0.75,
+                expected_similarity=0.5,
             ),
             param(
                 pixels1=[RED, RED, WHITE, WHITE],

src/testing/end_to_end/honeydew/honeydew/affordances/ui/screenshot/types.py

@@ -221,8 +221,7 @@ def _get_pixel_at_offset(self, offset: int) -> ui_types.Pixel:
             red=self.data[offset + 0],
             green=self.data[offset + 1],
             blue=self.data[offset + 2],
-            # TODO(b/399391948): Ignore pixel alpha values until we remove opacity-based brightness.
-            alpha=255,
+            alpha=self.data[offset + 3],
         )
 
     def _pixel_count(self) -> int: