Componentize component_updater: Replace content::BrowserThread usage with task runners

chrome/browser/component_updater/cld_component_installer.cc

Index: chrome/browser/component_updater/cld_component_installer.cc
diff --git a/chrome/browser/component_updater/cld_component_installer.cc b/chrome/browser/component_updater/cld_component_installer.cc
index d63b2da645bc18314c26083c43688c74abbfe57a..c27fd5adfe0f841bf2e387415a1eaecbf9bcd8e5 100644
--- a/chrome/browser/component_updater/cld_component_installer.cc
+++ b/chrome/browser/component_updater/cld_component_installer.cc
@@ -13,14 +13,13 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/path_service.h"
-#include "chrome/browser/profiles/profile.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "components/component_updater/component_updater_paths.h"
 #include "components/translate/content/browser/data_file_browser_cld_data_provider.h"
 #include "content/public/browser/browser_thread.h"
 #include "net/ssl/ssl_config_service.h"
 
 using component_updater::ComponentUpdateService;
-using content::BrowserThread;
 
 namespace {
 // TODO(andrewhayden): Make the data file path into a gyp/gn define
@@ -106,8 +105,12 @@ void RegisterCldComponent(ComponentUpdateService* cus) {
   scoped_ptr<ComponentInstallerTraits> traits(
       new CldComponentInstallerTraits());
   // |cus| will take ownership of |installer| during installer->Register(cus).
-  DefaultComponentInstaller* installer =
-      new DefaultComponentInstaller(traits.Pass());
+  DefaultComponentInstaller* installer = new DefaultComponentInstaller(
+      traits.Pass(),
+      content::BrowserThread::GetBlockingPool()
+          ->GetSequencedTaskRunnerWithShutdownBehavior(
+              content::BrowserThread::GetBlockingPool()->GetSequenceToken(),

[blundell, 2014/07/15 08:45:20]

What logic is behind the choices on lines 112 and 113 (and elsewhere throughout
this CL)?

[tommycli, 2014/07/15 18:58:25]

I replicated the choices made here: 

https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/com...

In another version of this patch, which I didn't upload, I used:
  ComponentUpdateService::GetConfig()->GetSequencedTaskRunner(), but this
requires adding a GetConfig method to ComponentUpdateService.

Do you prefer that?

+              base::SequencedWorkerPool::SKIP_ON_SHUTDOWN));
   installer->Register(cus);
 }