[Extensions] Re-enable File API tests.

ExtensionApiTest.FileAPI was disabled many years ago for a Webkit
roll issue and should have been re-enabled once that was fixed.

ExtensionApiTest.XHROnPersistentFileSystem was flaky on Linux, but
was disabled on all platforms. It showed no flakiness on any
platform.

Bug: 671144
Change-Id: I34345161bcc9d2c19579ad76e0293fba8adf3859
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2268643Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#783105}

chrome/browser/extensions/extension_fileapi_apitest.cc

@@ -7,12 +7,11 @@
 
 namespace extensions {
 
-IN_PROC_BROWSER_TEST_F(ExtensionApiTest, DISABLED_FileAPI) {
+IN_PROC_BROWSER_TEST_F(ExtensionApiTest, FileAPI) {
   ASSERT_TRUE(RunExtensionTest("fileapi")) << message_;
 }
 
-// crbug.com/671144
-IN_PROC_BROWSER_TEST_F(ExtensionApiTest, DISABLED_XHROnPersistentFileSystem) {
+IN_PROC_BROWSER_TEST_F(ExtensionApiTest, XHROnPersistentFileSystem) {
   ASSERT_TRUE(RunPlatformAppTest("xhr_persistent_fs")) << message_;
 }