With --isolate-extensions, forking (via OpenURL) for extensions is not needed.

chrome/browser/extensions/api/extension_action/browser_action_apitest.cc

Index: chrome/browser/extensions/api/extension_action/browser_action_apitest.cc
diff --git a/chrome/browser/extensions/api/extension_action/browser_action_apitest.cc b/chrome/browser/extensions/api/extension_action/browser_action_apitest.cc
index da79d2e5d26df0ac300c98ed66458ca757ba68a8..e464c23f3f4c8a01401436984088bacc9e5275f6 100644
--- a/chrome/browser/extensions/api/extension_action/browser_action_apitest.cc
+++ b/chrome/browser/extensions/api/extension_action/browser_action_apitest.cc
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
+#include "chrome/browser/download/download_shelf.h"
 #include "chrome/browser/extensions/api/extension_action/extension_action_api.h"
 #include "chrome/browser/extensions/browser_action_test_util.h"
 #include "chrome/browser/extensions/extension_action.h"
@@ -26,7 +27,6 @@
 #include "chrome/browser/ui/browser_navigator_params.h"
 #include "chrome/browser/ui/browser_window.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
-#include "chrome/common/extensions/extension_process_policy.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/test/base/ui_test_utils.h"
@@ -856,24 +856,38 @@ class NavigatingExtensionPopupBrowserTest : public BrowserActionApiTest {
   void TestPopupNavigationViaGet(
       const GURL& target_url,
       ExpectedNavigationStatus expected_navigation_status) {
-    std::string navigation_starting_script =
-        "window.location = '" + target_url.spec() + "';\n";
     TestPopupNavigation(target_url, expected_navigation_status,
-                        navigation_starting_script);
+                        CreateNavigationScriptForGet(target_url));
   }
 
   void TestPopupNavigationViaPost(
       const GURL& target_url,
       ExpectedNavigationStatus expected_navigation_status) {
-    std::string navigation_starting_script =
-        "var form = document.getElementById('form');\n"
-        "form.action = '" + target_url.spec() + "';\n"
-        "form.submit();\n";
     TestPopupNavigation(target_url, expected_navigation_status,
-                        navigation_starting_script);
+                        CreateNavigationScriptForPost(target_url));
+  }
+
+  void TestPopupDownloadViaGet(const GURL& target_url) {
+    TestPopupDownload(target_url, CreateNavigationScriptForGet(target_url));
+  }
+
+  void TestPopupDownloadViaPost(const GURL& target_url) {
+    TestPopupDownload(target_url, CreateNavigationScriptForPost(target_url));
   }
 
  private:
+  std::string CreateNavigationScriptForGet(const GURL& target_url) {
+    return "window.location = '" + target_url.spec() + "';\n";
+  }
+
+  std::string CreateNavigationScriptForPost(const GURL& target_url) {
+    return "var form = document.getElementById('form');\n"
+           "form.action = '" +
+           target_url.spec() +
+           "';\n"
+           "form.submit();\n";
+  }
+
   void TestPopupNavigation(const GURL& target_url,
                            ExpectedNavigationStatus expected_navigation_status,
                            std::string navigation_starting_script) {
@@ -945,6 +959,44 @@ class NavigatingExtensionPopupBrowserTest : public BrowserActionApiTest {
     }
   }
 
+  void TestPopupDownload(const GURL& target_url,
+                         std::string navigation_starting_script) {
+    content::DownloadTestObserverTerminal downloads_observer(
+        content::BrowserContext::GetDownloadManager(browser()->profile()),
+        1,  // == wait_count (only waiting for a single file).
+        content::DownloadTestObserver::ON_DANGEROUS_DOWNLOAD_FAIL);
+
+    // Override the default downloads directory, so that the test can cleanup
+    // after itself.  This section is based on CreateAndSetDownloadsDirectory
+    // method defined in a few other source files with tests.
+    std::unique_ptr<base::ScopedTempDir> downloads_directory =
+        CreateAndSetDownloadsDirectory(browser()->profile()->GetPrefs());
+    ASSERT_TRUE(downloads_directory);
+
+    // Navigate to a URL that will trigger a download (i.e. by replying with
+    // Content-Disposition: attachment; filename=...
+    // header).
+    TestPopupNavigation(target_url, EXPECTING_NAVIGATION_FAILURE,
+                        navigation_starting_script);
+
+    // Verify that a single file got downloaded.
+    downloads_observer.WaitForFinished();
+    EXPECT_EQ(0u, downloads_observer.NumDangerousDownloadsSeen());
+    EXPECT_EQ(1u, downloads_observer.NumDownloadsSeenInState(
+                      content::DownloadItem::COMPLETE));
+    EXPECT_TRUE(base::PathExists(downloads_directory->GetPath().AppendASCII(
+        "download-test3-attachment.gif")));
+
+#if !defined(OS_CHROMEOS)
+    // The test verification below is applicable only to scenarios where the
+    // download shelf is supported - on ChromeOS, instead of the download shelf,
+    // there is a download notification in the right-bottom corner of the
+    // screen.
+    EXPECT_TRUE(browser()->window()->IsDownloadShelfVisible());
+    browser()->window()->GetDownloadShelf()->Hide();
+#endif
+  }
+
   const Extension* popup_extension_;
   const Extension* other_extension_;
 };
@@ -985,51 +1037,14 @@ IN_PROC_BROWSER_TEST_F(NavigatingExtensionPopupBrowserTest,
 // Tests that navigating an extension pop-up to a http URI that returns
 // Content-Disposition: attachment; filename=...
 // works: No navigation, but download shelf visible + download goes through.
-//
-// Note - there is no "...ViaGet" flavour of this test, because we don't care
-// (yet) if GET succeeds with the download or not (it probably should succeed
-// for consistency with POST, but it always failed in M54 and before).  After
-// abandoing ShouldFork/OpenURL for all methods (not just for POST) [see comment
-// about https://crbug.com/646261 in ChromeContentRendererClient::ShouldFork]
-// GET should automagically start working for downloads.
-// TODO(lukasza): https://crbug.com/650694: Add a "Get" flavour of the test once
-// the download works both for GET and POST requests.
-IN_PROC_BROWSER_TEST_F(NavigatingExtensionPopupBrowserTest, DownloadViaPost) {
-  // Override the default downloads directory, so that the test can cleanup
-  // after itself.  This section is based on CreateAndSetDownloadsDirectory
-  // method defined in a few other source files with tests.
-  base::ThreadRestrictions::ScopedAllowIO allow_io;
-  std::unique_ptr<base::ScopedTempDir> downloads_directory =
-      CreateAndSetDownloadsDirectory(browser()->profile()->GetPrefs());
-  ASSERT_TRUE(downloads_directory);
-
-  // Setup monitoring of the downloads.
-  content::DownloadTestObserverTerminal downloads_observer(
-      content::BrowserContext::GetDownloadManager(browser()->profile()),
-      1,  // == wait_count (only waiting for "download-test3.gif").
-      content::DownloadTestObserver::ON_DANGEROUS_DOWNLOAD_FAIL);
-
+IN_PROC_BROWSER_TEST_F(NavigatingExtensionPopupBrowserTest, Download) {
   // Navigate to a URL that replies with
   // Content-Disposition: attachment; filename=...
   // header.
   GURL download_url(
       embedded_test_server()->GetURL("foo.com", "/download-test3.gif"));
-  TestPopupNavigationViaPost(download_url, EXPECTING_NAVIGATION_FAILURE);
-
-  // Verify that "download-test3.gif got downloaded.
-  downloads_observer.WaitForFinished();
-  EXPECT_EQ(0u, downloads_observer.NumDangerousDownloadsSeen());
-  EXPECT_EQ(1u, downloads_observer.NumDownloadsSeenInState(
-                    content::DownloadItem::COMPLETE));
-  EXPECT_TRUE(base::PathExists(downloads_directory->GetPath().AppendASCII(
-      "download-test3-attachment.gif")));
-
-  // The test verification below is applicable only to scenarios where the
-  // download shelf is supported - on ChromeOS, instead of the download shelf,
-  // there is a download notification in the right-bottom corner of the screen.
-#if !defined(OS_CHROMEOS)
-  EXPECT_TRUE(browser()->window()->IsDownloadShelfVisible());
-#endif
+  TestPopupDownloadViaGet(download_url);
+  TestPopupDownloadViaPost(download_url);
 }
 
 }  // namespace