Depend on the WebRTC component.

Starting from [1], WebRTC supports the Chromium component build and
direct dependencies on //third_party/webrtc are disallowed.
A dependency on //third_party/webrtc_overrides:webrtc_component is
required instead.

[1] - https://chromium-review.googlesource.com/c/chromium/src/+/1874722

Bug: webrtc:9419
Change-Id: I8a09d9d2c9a54ff45950b03779832e231213d215
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917204Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716093}

ios/web/web_view_only/BUILD.gn

@@ -37,7 +37,11 @@ source_set("unittests") {
     "//base",
     "//ios/web/public/web_view_only",
     "//ios/web/test:test_support",
-    "//third_party/webrtc/rtc_base",
+
+    # Even if this target doesn't depend on WebRTC, this dependency
+    # is needed in order to workaround a dependency issue among
+    # mojom components.
+    "//third_party/webrtc_overrides:webrtc_component",
   ]
 
   visibility = [