Move OnCustomInstall body to SequencedTaskRunner

Currently, OnCustomInstall is invoked in a background thread but it
invokes imageloader on UI thread which does not bring any known benefits.

We move imageloader operation from UI thread over a SequnecedTaskRunner.

BUG=chromium:780201
TEST=install is successful on DUT

Change-Id: I8deb2ebae9ff22fcf992f4c34d6198ddbcad0c70
Reviewed-on: https://chromium-review.googlesource.com/752622Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Xiaochu Liu <xiaochu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515291}

chrome/browser/component_updater/cros_component_installer.cc

@@ -10,6 +10,7 @@
 #include "base/optional.h"
 #include "base/path_service.h"
 #include "base/task_scheduler/post_task.h"
+#include "base/task_scheduler/task_traits.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/component_updater/component_installer_errors.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
@@ -34,14 +35,11 @@
      {"sha2hashstr",                                                         \
       "6d24de30f671da5aee6d463d9e446cafe9ddac672800a9defe86877dcde6c466"}}}};
 
-using content::BrowserThread;
-
 namespace component_updater {
 
 using ConfigMap = std::map<std::string, std::map<std::string, std::string>>;
 
 void LogRegistrationResult(base::Optional<bool> result) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   if (!result.has_value()) {
     DVLOG(1) << "Call to imageloader service failed.";
     return;
@@ -55,7 +53,6 @@ void LogRegistrationResult(base::Optional<bool> result) {
 void ImageLoaderRegistration(const std::string& version,
                              const base::FilePath& install_dir,
                              const std::string& name) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   chromeos::ImageLoaderClient* loader =
       chromeos::DBusThreadManager::Get()->GetImageLoaderClient();
   if (loader) {
@@ -82,8 +79,13 @@ CrOSComponentInstallerPolicy::CrOSComponentInstallerPolicy(
     cell = stoul(strstream.substr(0, 2), nullptr, 16);
     strstream.erase(0, 2);
   }
+  task_runner_ = base::CreateSingleThreadTaskRunnerWithTraits(
+      {base::MayBlock(), base::TaskPriority::BACKGROUND,
+       base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN});
 }
 
+CrOSComponentInstallerPolicy::~CrOSComponentInstallerPolicy() {}
+
 bool CrOSComponentInstallerPolicy::SupportsGroupPolicyEnabledComponentUpdates()
     const {
   return true;
@@ -101,9 +103,8 @@ CrOSComponentInstallerPolicy::OnCustomInstall(
   if (!manifest.GetString("version", &version)) {
     return ToInstallerResult(update_client::InstallError::GENERIC_ERROR);
   }
-  BrowserThread::PostTask(
-      BrowserThread::UI, FROM_HERE,
-      base::BindOnce(&ImageLoaderRegistration, version, install_dir, name));
+  task_runner_->PostTask(FROM_HERE, base::BindOnce(&ImageLoaderRegistration,
+                                                   version, install_dir, name));
   return update_client::CrxInstaller::Result(update_client::InstallError::NONE);
 }
 

chrome/browser/component_updater/cros_component_installer.h

@@ -10,6 +10,7 @@
 #include <string>
 #include <vector>
 
+#include "base/sequenced_task_runner.h"
 #include "chromeos/dbus/dbus_method_call_status.h"
 #include "components/component_updater/component_installer.h"
 #include "components/component_updater/component_updater_service.h"
@@ -45,7 +46,7 @@ struct ComponentConfig {
 class CrOSComponentInstallerPolicy : public ComponentInstallerPolicy {
  public:
   explicit CrOSComponentInstallerPolicy(const ComponentConfig& config);
-  ~CrOSComponentInstallerPolicy() override {}
+  ~CrOSComponentInstallerPolicy() override;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(CrOSComponentInstallerTest, IsCompatibleOrNot);
@@ -76,6 +77,8 @@ class CrOSComponentInstallerPolicy : public ComponentInstallerPolicy {
   std::string name;
   std::string env_version;
   uint8_t kSha2Hash_[crypto::kSHA256Length] = {};
+  // Use task_runner_ for scheduling all imageloader operations.
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(CrOSComponentInstallerPolicy);
 };