[Extensions] Re-enable a Download API test on Mac.

The DownloadExtensionTest_Download_InvalidURLs was timing out
on Mac and causing a free-after-use issue on Asan builds.
Splitting the test into two parts has fixed the issue with
timeouts. The Asan failure is no longer present.

The tests passed 3000 iterations on the bots without any issues.

Bug: 392288
Change-Id: I90416d1fc9e0a6621f6ea3b3bf737a66cc2bb5ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2229321
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780121}

chrome/browser/extensions/api/downloads/downloads_api_browsertest.cc

@@ -1993,19 +1993,10 @@ IN_PROC_BROWSER_TEST_F(DownloadExtensionTest,
       download_url.c_str())).c_str());
 }
 
-// flaky on mac: crbug.com/392288
-#if defined(OS_MACOSX)
-#define MAYBE_DownloadExtensionTest_Download_InvalidURLs \
-        DISABLED_DownloadExtensionTest_Download_InvalidURLs
-#else
-#define MAYBE_DownloadExtensionTest_Download_InvalidURLs \
-        DownloadExtensionTest_Download_InvalidURLs
-#endif
-
 class DownloadExtensionTestWithFtp : public DownloadExtensionTest {
  public:
   DownloadExtensionTestWithFtp() {
-    // DownloadExtensionTest_Download_InvalidURLs requires FTP support.
+    // DownloadExtensionTest_Download_InvalidURLs2 requires FTP support.
     // TODO(https://crbug.com/333943): Remove FTP tests and FTP feature flags.
     scoped_feature_list_.InitAndEnableFeature(features::kFtpProtocol);
   }
@@ -2016,27 +2007,27 @@ class DownloadExtensionTestWithFtp : public DownloadExtensionTest {
 
 // Test that downloading invalid URLs immediately returns kInvalidURLError.
 IN_PROC_BROWSER_TEST_F(DownloadExtensionTestWithFtp,
-                       MAYBE_DownloadExtensionTest_Download_InvalidURLs) {
-  LoadExtension("downloads_split");
-  GoOnTheRecord();
-
-  static const char* const kInvalidURLs[] = {
-    "foo bar",
-    "../hello",
-    "/hello",
-    "http://",
-    "#frag",
-    "foo/bar.html#frag",
-    "google.com/",
+                       DownloadExtensionTest_Download_InvalidURLs1) {
+  static constexpr const char* kInvalidURLs[] = {
+      "foo bar", "../hello",          "/hello",      "http://",
+      "#frag",   "foo/bar.html#frag", "google.com/",
   };
 
-  for (size_t index = 0; index < base::size(kInvalidURLs); ++index) {
+  for (const char* url : kInvalidURLs) {
     EXPECT_STREQ(errors::kInvalidURL,
-                  RunFunctionAndReturnError(new DownloadsDownloadFunction(),
-                                            base::StringPrintf(
-        "[{\"url\": \"%s\"}]", kInvalidURLs[index])).c_str())
-      << kInvalidURLs[index];
+                 RunFunctionAndReturnError(
+                     new DownloadsDownloadFunction(),
+                     base::StringPrintf("[{\"url\": \"%s\"}]", url))
+                     .c_str())
+        << url;
   }
+}
+
+// Test various failure modes for downloading invalid URLs.
+IN_PROC_BROWSER_TEST_F(DownloadExtensionTestWithFtp,
+                       DownloadExtensionTest_Download_InvalidURLs2) {
+  LoadExtension("downloads_split");
+  GoOnTheRecord();
 
   int result_id = -1;
   std::unique_ptr<base::Value> result(RunFunctionAndReturnResult(