MD Downloads: track downloads in C++, dispatch discrete JS updates

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 591dda9760e7c76c5d5e0ebe6058d03886a73be8..5c92529f7c5dc75b90fbb7c48fb730cc8ca2d9b5 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -1610,7 +1610,6 @@ test("unit_tests") {
 
   if (!is_ios) {
     deps += [
-      ":unit_tests_js",
       "//components/autofill/content/browser/wallet:test_support",
       "//components/autofill/content/renderer:test_support",
       "//components/data_reduction_proxy/core/browser:test_support",
@@ -1666,6 +1665,7 @@ test("unit_tests") {
   }
 
   if (!is_android && !is_ios) {
+    deps += [ ":unit_tests_js" ]
     sources += rebase_path(
             chrome_tests_unit_gypi_values.chrome_unit_tests_non_mobile_sources,
             ".",