Move on-demand update checks from the FILE thread to the blocking pool.

chrome/browser/google/google_update_win.h

Index: chrome/browser/google/google_update_win.h
diff --git a/chrome/browser/google/google_update_win.h b/chrome/browser/google/google_update_win.h
index 33760ca2de5338017075da3875b12b241917cee5..b8f59e978d33c42dba72cdcb15ec454c79d402e0 100644
--- a/chrome/browser/google/google_update_win.h
+++ b/chrome/browser/google/google_update_win.h
@@ -14,7 +14,7 @@
 #include "ui/gfx/native_widget_types.h"
 
 namespace base {
-class SingleThreadTaskRunner;
+class SequencedTaskRunner;
 }  // namespace base
 
 // These values are used for a histogram. Do not reorder.
@@ -91,23 +91,28 @@ class UpdateCheckDelegate {
 // available and |install_update_if_possible| is true, the new version will be
 // automatically downloaded and installed. |elevation_window| is the window
 // which should own any necessary elevation UI. Methods on |delegate| will be
-// invoked on the caller's thread to provide feedback on the operation, with
+// invoked on the caller's sequence to provide feedback on the operation, with

[Peter Kasting, 2016/08/03 01:24:34]

Nit: sequence -> task runner?  (I think of "sequenced" as an adjective
describing the task runner behavior rather than "sequence" being a noun you can
invoke things on.)

This also applies in other places where you've used similar language.

[grt (UTC plus 2), 2016/08/03 05:36:31]

Done.

 // messages localized to |locale| if possible.
-void BeginUpdateCheck(
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner,
-    const std::string& locale,
-    bool install_update_if_possible,
-    gfx::AcceleratedWidget elevation_window,
-    const base::WeakPtr<UpdateCheckDelegate>& delegate);
+void BeginUpdateCheck(scoped_refptr<base::SequencedTaskRunner> task_runner,
+                      const std::string& locale,
+                      bool install_update_if_possible,
+                      gfx::AcceleratedWidget elevation_window,
+                      const base::WeakPtr<UpdateCheckDelegate>& delegate);
+
+// A type of callback supplied by tests to provide a custom

[Peter Kasting, 2016/08/03 01:24:34]

Nit: You're welcome to omit "A type of callback" on these next two comments if
you want, since it's kinda obvious.

[grt (UTC plus 2), 2016/08/03 05:36:30]

Acknowledged.

+// IGlobalInterfaceTable implementation.
+using GlobalInterfaceTableClassFactory =
+    base::Callback<HRESULT(base::win::ScopedComPtr<IGlobalInterfaceTable>*)>;
 
 // A type of callback supplied by tests to provide a custom IGoogleUpdate3Web
 // implementation (see src/google_update/google_update_idl.idl).
-typedef base::Callback<HRESULT(base::win::ScopedComPtr<IGoogleUpdate3Web>*)>
-    GoogleUpdate3ClassFactory;
+using GoogleUpdate3ClassFactory =
+    base::Callback<HRESULT(base::win::ScopedComPtr<IGoogleUpdate3Web>*)>;
 
-// For use by tests that wish to provide a custom IGoogleUpdate3Web
-// implementation independent of Google Update's.
-void SetGoogleUpdateFactoryForTesting(
+// For use by tests that wish to provide custom IGlobalInterfaceTable and
+// IGoogleUpdate3Web implementations.
+void SetUpdateCheckFactoriesForTesting(
+    const GlobalInterfaceTableClassFactory& git_factory,
     const GoogleUpdate3ClassFactory& google_update_factory);
 
 #endif  // CHROME_BROWSER_GOOGLE_GOOGLE_UPDATE_WIN_H_