Enable -Wextra-semi in chromecast builds.

This seems to work after https://chromium-review.googlesource.com/c/chromium/src/+/1483332

Bug: 926235
Change-Id: I5a73ea6bf72a095be9222599b35b9544cfca3c73
Reviewed-on: https://chromium-review.googlesource.com/c/1486714
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Sergey Volk <servolk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635518}

build/config/compiler/BUILD.gn

@@ -1590,8 +1590,7 @@ config("chromium_code") {
 
     # TODO(thakis): Enable this for more platforms, https://crbug.com/926235
     has_dchecks = is_debug || dcheck_always_on
-    if (has_dchecks &&
-        ((is_linux && !is_chromecast && !use_libfuzzer) || is_mac)) {
+    if (has_dchecks && ((is_linux && !use_libfuzzer) || is_mac)) {
       cflags += [ "-Wextra-semi" ]
     }
   }