Fix content_shell_lib component build on chromecast platform

This fixes the following error in components builds on chromecast:

ld.lld: error: undefined symbol: media::mojom::kMediaRendererServiceName
>>> referenced by shell_content_browser_client.cc:301 (../../content/shell/browser/shell_content_browser_client.cc:301)
>>>               content_shell_lib/shell_content_browser_client.o:(content::ShellContentBrowserClient::RunServiceInstance(service_manager::Identity const&, mojo::PendingReceiver<service_manager::mojom::Service>*)) in archive obj/content/shell/libcontent_shell_lib.a
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Change-Id: I4fa28fead6e003b1bfc9fe0448c53acf56864b6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1874331Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708680}

content/shell/BUILD.gn

@@ -478,6 +478,10 @@ jumbo_static_library("content_shell_lib") {
       "browser/shell_plugin_service_filter.h",
     ]
   }
+
+  if (enable_cast_renderer) {
+    deps += [ "//media/mojo/mojom:constants" ]
+  }
 }
 
 grit("content_shell_resources_grit") {