LibGfx: add erroneous cases to GIF test suite

Author: https://github.com/peterdn
Commit: https://github.com/SerenityOS/serenity/commit/cd38fab63f6
Pull-request: https://github.com/SerenityOS/serenity/pull/3998

Base/res/html/misc/gifsuite.html

@@ -140,6 +140,42 @@
   <td>Transparent gif with 4 transparent frames, loops forever, restore previous</td>
  </tr>
 
+ <tr>
+  <td class="b"><img src="gifsuite_files/animated_transparent_loop_frames_out_of_bounds.gif"></td>
+  <td class="b"><img src="gifsuite_files/animated_transparent_loop_frames_out_of_bounds-0.png"></td>
+  <td class="b"><img src="gifsuite_files/animated_transparent_loop_frames_out_of_bounds-1.png"></td>
+  <td class="b"><img src="gifsuite_files/animated_transparent_loop_frames_out_of_bounds-2.png"></td>
+  <td class="b"><img src="gifsuite_files/animated_transparent_loop_frames_out_of_bounds-3.png"></td>
+  <td>
+    <p><strong>Erroneous test case:</strong> frame out-of-bounds.
+    The first frame is located at offset (200,0) and so is wholly outside of the bounds of the 100x100 GIF.
+    The last frame is partially out of bounds, located at (60,60) and of size (50,50).</p>
+
+    <p>Note that the GIF specification is unclear on what to do if a frame extends past the logical
+    screen of the GIF, therefore different renderers behave differently here:</p>
+
+    <ul>
+      <li>Firefox, ImageMagick: don't expand logical screen, render unwritten pixels as transparent
+        <strong>(this is what the reference frames show)</strong>
+      <li>Chrome, Edge, IE11: expand logical screen, render unwritten pixels as transparent
+      <li>Safari: don't expand logical screen, render unwritten pixels as GIF background colour
+    </ul>
+  </td>
+ </tr>
+
+ <tr>
+  <td class="b"><img src="gifsuite_files/bad_lzw_data.gif"></td>
+  <td class="b">N/A</td>
+  <td class="b">N/A</td>
+  <td class="b">N/A</td>
+  <td class="b">N/A</td>
+  <td>
+    <p><strong>Erroneous test case:</strong>. Final frame contains bad LZW data and will fail to decode.
+    Decoder implementations are not under any obligation to render anything useful here, however they
+    should fail gracefully and not crash.</p>
+  </td>
+ </tr>
+
 </tbody>
 </table>