[TWA] Enable TWA postmessage flag

Enable TWA postMessage flag to release the feature.

(cherry picked from commit 5f7d88f)

Bug: 1451777
Change-Id: I3710cc3bb8a79f9e42a05751d455379cf4f09317
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4593720
Reviewed-by: Peter Conn <peconn@chromium.org>
Commit-Queue: Sayed Elabady <elabadysayed@chromium.org>
Commit-Queue: Peter Conn <peconn@chromium.org>
Auto-Submit: Sayed Elabady <elabadysayed@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1153841}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4598150
Reviewed-by: Michael van Ouwerkerk <mvanouwerkerk@chromium.org>
Commit-Queue: Michael van Ouwerkerk <mvanouwerkerk@chromium.org>
Cr-Commit-Position: refs/branch-heads/5790@{#485}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

chrome/browser/flags/android/chrome_feature_list.cc

@@ -1040,7 +1040,7 @@ BASE_FEATURE(kToolbarScrollAblationAndroid,
 
 BASE_FEATURE(kTrustedWebActivityPostMessage,
              "TrustedWebActivityPostMessage",
-             base::FEATURE_DISABLED_BY_DEFAULT);
+             base::FEATURE_ENABLED_BY_DEFAULT);
 
 BASE_FEATURE(kResizeOnlyActiveTab,
              "ResizeOnlyActiveTab",