[Trusted Types] Enable the Blink-side flag.

Following up on https://chromium-review.googlesource.com/c/chromium/src/+/2095548,
which set the //content-side flag. This should be a
no-op if things are wired up correctly.

Bug: 739170
Change-Id: I91f977ab6bd472c3e8f1fdcae48a0dfbb4a070a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120416Reviewed-by: Yifan Luo <lyf@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753253}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1715,7 +1715,7 @@
     },
     {
       name: "TrustedDOMTypes",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "TrustTokens",