[iOS] Define global assert_no_deps and use it to prevent regressions.

components/BUILD.gn

Index: components/BUILD.gn
diff --git a/components/BUILD.gn b/components/BUILD.gn
index 67d9218500ebf0394158d9f1869608d2fc548938..54f2799d6806ee0ca8dbf8383fe1958b9e91225d 100644
--- a/components/BUILD.gn
+++ b/components/BUILD.gn
@@ -11,6 +11,10 @@ if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
+if (is_ios) {
+  import("//ios/build/config.gni")
+}
+
 # To add a unit test to this target, make a "unit_test" source_set in your
 # component (it's important to use a source_set instead of a static library or
 # no tests will run) and add a reference here. You can add more than one unit
@@ -264,6 +268,10 @@ test("components_unittests") {
   if (safe_browsing_mode == 2) {
     deps += [ "//components/safe_browsing_db:unit_tests_mobile" ]
   }
+
+  if (is_ios) {
+    assert_no_deps = ios_assert_no_deps
+  }
 }
 
 repack("components_tests_pak") {