Avoid file IO on UI thread by moving more save-page-as stuff to the FILE thread.

chrome/browser/download/save_page_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.
 
 #include <stddef.h>
 #include <stdint.h>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/test_file_util.h"
+#include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/download/chrome_download_manager_delegate.h"
 #include "chrome/browser/download/download_history.h"
 #include "chrome/browser/download/download_prefs.h"
 #include "chrome/browser/download/download_service.h"
 #include "chrome/browser/download/download_service_factory.h"
 #include "chrome/browser/download/save_package_file_picker.h"
 #include "chrome/browser/net/url_request_mock_util.h"
 #include "chrome/browser/profiles/profile.h"
@@ skipping 686 matching lines @@
       "Test page for saving page feature.mhtml"));
   SavePackageFilePicker::SetShouldPromptUser(false);
   DownloadPersistedObserver persisted(browser()->profile(), base::Bind(
       &DownloadStoredProperly, url, full_file_name, -1,
       history::DownloadState::COMPLETE));
   scoped_refptr<content::MessageLoopRunner> loop_runner(
       new content::MessageLoopRunner);
   SavePackageFinishedObserver observer(
       content::BrowserContext::GetDownloadManager(browser()->profile()),
       loop_runner->QuitClosure());
+  bool old_io_allowed_value = base::ThreadRestrictions::SetIOAllowed(false);
   chrome::SavePage(browser());
   loop_runner->Run();
+  base::ThreadRestrictions::SetIOAllowed(old_io_allowed_value);

[Łukasz Anforowicz, 2016/07/26 22:30:50]

I've reverted these changes in a more recent patchset - I am instead doing the
IO asserts on a broader scale in https://codereview.chromium.org/2175933002/
(this is for content_browsertests;  if this goes well, then maybe I'll also try
chrome layer's browser_tests in https://codereview.chromium.org/2175933002).

   ASSERT_TRUE(VerifySavePackageExpectations(browser(), url));
   persisted.WaitForPersisted();
 
   ASSERT_TRUE(base::PathExists(full_file_name));
   int64_t actual_file_size = -1;
   EXPECT_TRUE(base::GetFileSize(full_file_name, &actual_file_size));
   EXPECT_LE(kFileSizeMin, actual_file_size);
 
   std::string contents;
   EXPECT_TRUE(base::ReadFileToString(full_file_name, &contents));
   // Test for a CSS encoded character.  This used to use HTML encoding.
   EXPECT_THAT(contents, HasSubstr("content: \"\\e003 \\e004 b\""));
 }
 
 IN_PROC_BROWSER_TEST_F(SavePageBrowserTest, SavePageBrowserTest_NonMHTML) {
   SavePackageFilePicker::SetShouldPromptUser(false);
   GURL url("data:text/plain,foo");
   ui_test_utils::NavigateToURL(browser(), url);
   scoped_refptr<content::MessageLoopRunner> loop_runner(
       new content::MessageLoopRunner);
   SavePackageFinishedObserver observer(
       content::BrowserContext::GetDownloadManager(browser()->profile()),
       loop_runner->QuitClosure());
+  bool old_io_allowed_value = base::ThreadRestrictions::SetIOAllowed(false);
   chrome::SavePage(browser());
   loop_runner->Run();
+  base::ThreadRestrictions::SetIOAllowed(old_io_allowed_value);
   base::FilePath download_dir = DownloadPrefs::FromDownloadManager(
       GetDownloadManager())->DownloadPath();
   base::FilePath filename = download_dir.AppendASCII("dataurl.txt");
   ASSERT_TRUE(base::PathExists(filename));
   std::string contents;
   EXPECT_TRUE(base::ReadFileToString(filename, &contents));
   EXPECT_EQ("foo", contents);
 }
 
 // If a save-page-complete operation results in creating subresources that would
@@ skipping 489 matching lines @@
   TestOriginalVsSavedPage(save_page_type, url, 1, expected_substrings);
 }
 
 INSTANTIATE_TEST_CASE_P(
     SaveType,
     SavePageOriginalVsSavedComparisonTest,
     ::testing::Values(content::SAVE_PAGE_TYPE_AS_COMPLETE_HTML,
                       content::SAVE_PAGE_TYPE_AS_MHTML));
 
 }  // namespace