Disable Quarantine tests on platforms its not supported.

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index e07a00d8d22e5c2bc4c8e4ef8527cff69b96253e..1fd0646b30693e31918b5c69f44f8063c2089928 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
+import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
@@ -1318,7 +1319,6 @@ test("content_unittests") {
     "../common/plugin_list_unittest.cc",
     "../common/quarantine/quarantine_linux_unittest.cc",
     "../common/quarantine/quarantine_mac_unittest.mm",
-    "../common/quarantine/quarantine_unittest.cc",
     "../common/quarantine/quarantine_win_unittest.cc",
     "../common/sandbox_mac_compiler_unittest.mm",
     "../common/sandbox_mac_diraccess_unittest.mm",
@@ -1369,6 +1369,14 @@ test("content_unittests") {
     "run_all_unittests.cc",
   ]
 
+  # Chromecasts do not have extended attributes enabled; even if it were
+  # enabled, the devices use tmpfs which restricts the extended attributes that
+  # can be set such that quarantining still would not work. (The platform
+  # specific tests include a runtime guard to skip tests that need xattr.)
+  if (!is_chromecast) {
+    sources += [ "../common/quarantine/quarantine_unittest.cc" ]
+  }
+
   # ChromeOS also defines linux but their memory-monitors conflict.
   if (is_chromeos) {
     sources += [ "../browser/memory/memory_monitor_chromeos_unittest.cc" ]