[Extensions] Re-enable an ExtensionFetchTest.

The ExtensionCannotFetchHostedResourceWithoutHostPermissions is
no longer flaky.

Bug: 1038156
Change-Id: Iecadf163ddd5be64e296188352ae3a268fe715a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2140777Reviewed-by: Archana Simha <archanasimha@chromium.org>
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758542}

chrome/browser/extensions/fetch_apitest.cc

@@ -153,10 +153,9 @@ IN_PROC_BROWSER_TEST_F(ExtensionFetchTest,
                               "example.com", "/extensions/test_file.txt"))));
 }
 
-// TODO(crbug.com/1038156): Test is flaky.
 IN_PROC_BROWSER_TEST_F(
     ExtensionFetchTest,
-    DISABLED_ExtensionCannotFetchHostedResourceWithoutHostPermissions) {
+    ExtensionCannotFetchHostedResourceWithoutHostPermissions) {
   TestExtensionDir dir;
   constexpr char kManifest[] =
       R"({