Add absl::StatusOr to abseil TBD features

Bug: None
Change-Id: Ife9ebd44511859992b39e11ef13d3cba660317f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391063Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Danil Chapovalov <danilchap@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804225}

styleguide/c++/c++11.html

@@ -51,7 +51,10 @@ The current status of existing standards and Abseil features is:
 <li><b>C++14:</b> <i>Default allowed; see banned features below</i></li>
 <li><b>C++17:</b> <i>Not yet supported in Chromium, unlikely before mid-2021; <a href="http://crbug.com/752720">tracking bug</a></i></li>
 <li><b>C++20:</b> <i>Not yet standardized</i></li>
-<li><b>Abseil:</b> Initially supported July 31, 2020; see allowed/banned/TBD features below</li>
+<li><b>Abseil:</b> Initially supported July 31, 2020; see allowed/banned/TBD features below
+<ul>
+<li>absl::StatusOr: Initially supported September 3, 2020</li>
+</ul></li>
 </ul></p>
 
 
@@ -441,6 +444,14 @@ size_t index = absl::Uniform(bitgen, 0u, elems.size());</code></td>
 <td></td>
 </tr>
 
+<tr>
+<td>StatusOr</td>
+<td><code>absl::StatusOr&lt;T&gt;</td>
+<td>An object that is either a usable value, or an error Status explaining why such a value is not present.</td>
+<td><a href="https://source.chromium.org/chromium/chromium/src/+/master:third_party/abseil-cpp/absl/status/statusor.h">statusor.h</a></td>
+<td></td>
+</tr>
+
 <tr>
 <td>String Formatting</td>
 <td><code>absl::StrFormat</code>