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

chrome/browser/shell_integration.cc

Index: chrome/browser/shell_integration.cc
diff --git a/chrome/browser/shell_integration.cc b/chrome/browser/shell_integration.cc
index a846887aa0d8bb3a30a26c9878843fec0096d1bd..7d746c3eeb2f28f2dabf24cf0b64b1e787da6901 100644
--- a/chrome/browser/shell_integration.cc
+++ b/chrome/browser/shell_integration.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/shell_integration.h"
 
+#include "base//task_scheduler/post_task.h"

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

Extra /

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

Done.

 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/files/file_util.h"
@@ -136,15 +137,18 @@ base::string16 GetAppShortcutsSubdirName() {
 //
 
 void DefaultWebClientWorker::StartCheckIsDefault() {
-  BrowserThread::PostTask(
-      BrowserThread::FILE, FROM_HERE,
-      base::Bind(&DefaultWebClientWorker::CheckIsDefault, this, false));
+  base::CreateSequencedTaskRunnerWithTraits({base::MayBlock()})
+      ->PostTask(FROM_HERE, base::Bind(&DefaultWebClientWorker::CheckIsDefault,
+                                       this, false));
 }
 
 void DefaultWebClientWorker::StartSetAsDefault() {
-  BrowserThread::PostTask(
-      BrowserThread::FILE, FROM_HERE,
-      base::Bind(&DefaultWebClientWorker::SetAsDefault, this));
+  // TODO(pmonette): Windows' implementation uses a base::Timer which currently
+  // still requires a SingleThreadTaskRunner. Change this to a
+  // SequencedTaskRunner when crbug.com/552633 is fixed.
+  base::CreateSingleThreadTaskRunnerWithTraits({base::MayBlock()})
+      ->PostTask(FROM_HERE,
+                 base::Bind(&DefaultWebClientWorker::SetAsDefault, this));
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -171,7 +175,8 @@ void DefaultWebClientWorker::OnCheckIsDefaultComplete(
 // DefaultWebClientWorker, private:
 
 void DefaultWebClientWorker::CheckIsDefault(bool is_following_set_as_default) {
-  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+  base::ThreadRestrictions::AssertIOAllowed();
+
   DefaultWebClientState state = CheckIsDefaultImpl();
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
@@ -180,7 +185,7 @@ void DefaultWebClientWorker::CheckIsDefault(bool is_following_set_as_default) {
 }
 
 void DefaultWebClientWorker::SetAsDefault() {
-  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+  base::ThreadRestrictions::AssertIOAllowed();
 
   // SetAsDefaultImpl will make sure the callback is executed exactly once.
   SetAsDefaultImpl(