Remove the usage of BrowserThread::FILE in the shell_integration* files

chrome/browser/shell_integration_win.cc

Index: chrome/browser/shell_integration_win.cc
diff --git a/chrome/browser/shell_integration_win.cc b/chrome/browser/shell_integration_win.cc
index 6661fcef8312e7d26a207adccc547bdb9818650a..b46c436ec1db411b14107d11312c1fc515ae8c47 100644
--- a/chrome/browser/shell_integration_win.cc
+++ b/chrome/browser/shell_integration_win.cc
@@ -31,6 +31,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "base/win/registry.h"
@@ -53,12 +54,9 @@
 #include "chrome/installer/util/scoped_user_protocol_entry.h"
 #include "chrome/installer/util/shell_util.h"
 #include "components/variations/variations_associated_data.h"
-#include "content/public/browser/browser_thread.h"
 #include "content/public/browser/utility_process_mojo_client.h"
 #include "ui/base/l10n/l10n_util.h"
 
-using content::BrowserThread;
-
 namespace shell_integration {
 
 namespace {
@@ -149,8 +147,7 @@ base::string16 GetExpectedAppId(const base::CommandLine& command_line,
 }
 
 void MigrateTaskbarPinsCallback() {
-  // This should run on the file thread.
-  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+  base::ThreadRestrictions::AssertIOAllowed();
 
   // Get full path of chrome.
   base::FilePath chrome_exe;
@@ -327,8 +324,6 @@ class OpenSystemSettingsHelper {
   // watched. The array must contain at least one element.
   static void Begin(const wchar_t* const protocols[],
                     const base::Closure& on_finished_callback) {
-    DCHECK_CURRENTLY_ON(BrowserThread::FILE);

[Lei Zhang, 2017/05/19 23:23:13]

Looks like you wrote this code. If you are ok without any DCHECKs to help
enforce threading requirements, ok.

[Patrick Monette, 2017/05/26 01:50:12]

Your comment made me realize that there is actually a threading requirement for
the deletion of the OpenSystemSettingsHelper. I added a SequenceChecker.

-
     delete instance_;
     instance_ = new OpenSystemSettingsHelper(protocols, on_finished_callback);
   }
@@ -368,8 +363,6 @@ class OpenSystemSettingsHelper {
   //       function even if the value change is the only one that matters. This
   //       is good enough for now.
   void OnRegistryKeyChanged() {
-    DCHECK_CURRENTLY_ON(BrowserThread::FILE);
-
     // Make sure all the registry watchers have fired.
     if (--registry_watcher_count_ == 0) {
       UMA_HISTOGRAM_MEDIUM_TIMES(
@@ -384,8 +377,6 @@ class OpenSystemSettingsHelper {
   // |on_finished_callback_| and then dispose of this class instance to make
   // sure the callback won't get called subsequently.
   void ConcludeInteraction(ConcludeReason conclude_reason) {
-    DCHECK_CURRENTLY_ON(BrowserThread::FILE);
-
     UMA_HISTOGRAM_ENUMERATION(
         "DefaultBrowser.SettingsInteraction.ConcludeReason", conclude_reason,
         NUM_CONCLUDE_REASON_TYPES);
@@ -642,8 +633,6 @@ bool SetAsDefaultBrowserUsingIntentPicker() {
 
 void SetAsDefaultBrowserUsingSystemSettings(
     const base::Closure& on_finished_callback) {
-  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
-
   base::FilePath chrome_exe;
   if (!PathService::Get(base::FILE_EXE, &chrome_exe)) {
     NOTREACHED() << "Error getting app exe path";
@@ -690,7 +679,7 @@ bool SetAsDefaultProtocolClientUsingIntentPicker(const std::string& protocol) {
 void SetAsDefaultProtocolClientUsingSystemSettings(
     const std::string& protocol,
     const base::Closure& on_finished_callback) {
-  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+  base::ThreadRestrictions::AssertIOAllowed();
 
   base::FilePath chrome_exe;
   if (!PathService::Get(base::FILE_EXE, &chrome_exe)) {
@@ -730,14 +719,12 @@ void MigrateTaskbarPins() {
   if (base::win::GetVersion() < base::win::VERSION_WIN7)
     return;
 
-  // This needs to happen eventually (e.g. so that the appid is fixed and the
-  // run-time Chrome icon is merged with the taskbar shortcut), but this is not
-  // urgent and shouldn't delay Chrome startup.
-  static const int64_t kMigrateTaskbarPinsDelaySeconds = 15;
-  BrowserThread::PostDelayedTask(
-      BrowserThread::FILE, FROM_HERE,
-      base::Bind(&MigrateTaskbarPinsCallback),
-      base::TimeDelta::FromSeconds(kMigrateTaskbarPinsDelaySeconds));
+  // This needs to happen (e.g. so that the appid is fixed and the
+  // run-time Chrome icon is merged with the taskbar shortcut), but it is not an
+  // urgent task.
+  base::PostTaskWithTraits(FROM_HERE,
+                           {base::MayBlock(), base::TaskPriority::BACKGROUND},
+                           base::Bind(&MigrateTaskbarPinsCallback));
 }
 
 void GetIsPinnedToTaskbarState(