Disable all the tests that are flaking more than 5% on ChromeOS builders.

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

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Disable everything on windows only. http://crbug.com/306144
 #ifndef OS_WIN
 
 #include <algorithm>
 
 #include "base/file_util.h"
@@ skipping 785 matching lines @@
     return downloads::INTERRUPT_REASON_##name;
 #include "content/public/browser/download_interrupt_reason_values.h"
 #undef INTERRUPT_REASON
   }
   NOTREACHED();
   return downloads::INTERRUPT_REASON_NONE;
 }
 
 }  // namespace
 
+#if defined(OS_CHROMEOS)
+// http://crbug.com/396510
+#define MAYBE_DownloadExtensionTest_Open DISABLED_DownloadExtensionTest_Open
+#else
+#define MAYBE_DownloadExtensionTest_Open DownloadExtensionTest_Open
+#endif
 IN_PROC_BROWSER_TEST_F(DownloadExtensionTest,
-                       DownloadExtensionTest_Open) {
+                       MAYBE_DownloadExtensionTest_Open) {
   LoadExtension("downloads_split");
   DownloadsOpenFunction* open_function = new DownloadsOpenFunction();
   open_function->set_user_gesture(true);
   EXPECT_STREQ(errors::kInvalidId,
                RunFunctionAndReturnError(
                    open_function,
                    "[-42]").c_str());
 
   DownloadItem* download_item = CreateSlowTestDownload();
   ASSERT_TRUE(download_item);
@@ skipping 3300 matching lines @@
   EXPECT_EQ(downloads::FILENAME_CONFLICT_ACTION_PROMPT, conflict_action);
   EXPECT_FALSE(warnings.empty());
   EXPECT_EQ(ExtensionWarning::kDownloadFilenameConflict,
             warnings.begin()->warning_type());
   EXPECT_EQ("incumbent", warnings.begin()->extension_id());
 }
 
 }  // namespace extensions
 
 #endif  // http://crbug.com/3061144