Add a SUPPORTS_LOADING_MODE response header.

The response header is needed for a document to be loaded in a fenced frame: https://developer.chrome.com/docs/privacy-sandbox/fenced-frame/#server-opt-in.

RELNOTES=`net`: Added `SUPPORTS_LOADING_MODE` HTTP response header.
PiperOrigin-RevId: 462659126

android/guava/src/com/google/common/net/HttpHeaders.java

@@ -365,6 +365,16 @@ private ReferrerPolicyValues() {}
    */
   public static final String SOURCE_MAP = "SourceMap";
 
+  /**
+   * The HTTP <a href="https://github.com/WICG/nav-speculation/blob/main/opt-in.md">{@code
+   * Supports-Loading-Mode}</a> header field name. This can be used to specify, for example, <a
+   * href="https://developer.chrome.com/docs/privacy-sandbox/fenced-frame/#server-opt-in">fenced
+   * frames</a>.
+   *
+   * @since NEXT
+   */
+  public static final String SUPPORTS_LOADING_MODE = "Supports-Loading-Mode";
+
   /**
    * The HTTP <a href="http://tools.ietf.org/html/rfc6797#section-6.1">{@code
    * Strict-Transport-Security}</a> header field name.

guava/src/com/google/common/net/HttpHeaders.java

@@ -365,6 +365,16 @@ private ReferrerPolicyValues() {}
    */
   public static final String SOURCE_MAP = "SourceMap";
 
+  /**
+   * The HTTP <a href="https://github.com/WICG/nav-speculation/blob/main/opt-in.md">{@code
+   * Supports-Loading-Mode}</a> header field name. This can be used to specify, for example, <a
+   * href="https://developer.chrome.com/docs/privacy-sandbox/fenced-frame/#server-opt-in">fenced
+   * frames</a>.
+   *
+   * @since NEXT
+   */
+  public static final String SUPPORTS_LOADING_MODE = "Supports-Loading-Mode";
+
   /**
    * The HTTP <a href="http://tools.ietf.org/html/rfc6797#section-6.1">{@code
    * Strict-Transport-Security}</a> header field name.