Use TaskScheduler instead of WorkerPool in extension_printer_handler.cc.

The following traits are used:

Priority: Inherited (default)
  The priority is inherited from the calling context (i.e. TaskTraits
  are initialized with the priority of the current task).

Shutdown behavior: CONTINUE_ON_SHUTDOWN
  Tasks posted with this mode which have not started executing before
  shutdown is initiated will never run. Tasks with this mode running at
  shutdown will be ignored (the worker will not be joined).

  Note: Tasks that were previously posted to base::WorkerPool should
  use this shutdown behavior because this is how base::WorkerPool
  handles all its tasks.

May Block:
  Tasks posted with MayBlock() may block. This includes but is not
  limited to tasks that wait on synchronous file I/O operations:
  read or write a file from disk, interact with a pipe or a socket,
  rename or delete a file, enumerate files in a directory, etc. This
  trait isn't required for the mere use of locks.

BUG=659191

Review-Url: https://codereview.chromium.org/2604923002
Cr-Commit-Position: refs/heads/master@{#442953}

chrome/browser/ui/webui/print_preview/extension_printer_handler.cc

@@ -16,7 +16,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/strings/string_split.h"
-#include "base/task_runner_util.h"
+#include "base/task_scheduler/post_task.h"
 #include "chrome/browser/printing/pwg_raster_converter.h"
 #include "components/cloud_devices/common/cloud_device_description.h"
 #include "components/cloud_devices/common/printer_description.h"
@@ -69,10 +69,9 @@ UpdateJobFileInfoOnWorkerThread(
 
 // Callback to PWG raster conversion.
 // Posts a task to update print job with info about file containing converted
-// PWG raster data. The task is posted to |slow_task_runner|.
+// PWG raster data.
 void UpdateJobFileInfo(
     std::unique_ptr<extensions::PrinterProviderPrintJob> job,
-    const scoped_refptr<base::TaskRunner>& slow_task_runner,
     const ExtensionPrinterHandler::PrintJobCallback& callback,
     bool success,
     const base::FilePath& pwg_file_path) {
@@ -81,8 +80,11 @@ void UpdateJobFileInfo(
     return;
   }
 
-  base::PostTaskAndReplyWithResult(
-      slow_task_runner.get(), FROM_HERE,
+  base::PostTaskWithTraitsAndReplyWithResult(
+      FROM_HERE, base::TaskTraits()
+                     .WithShutdownBehavior(
+                         base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN)
+                     .MayBlock(),
       base::Bind(&UpdateJobFileInfoOnWorkerThread, pwg_file_path,
                  base::Passed(&job)),
       callback);
@@ -122,12 +124,8 @@ bool ParseProvisionalUsbPrinterId(const std::string& printer_id,
 }  // namespace
 
 ExtensionPrinterHandler::ExtensionPrinterHandler(
-    content::BrowserContext* browser_context,
-    const scoped_refptr<base::TaskRunner>& slow_task_runner)
-    : browser_context_(browser_context),
-      slow_task_runner_(slow_task_runner),
-      weak_ptr_factory_(this) {
-}
+    content::BrowserContext* browser_context)
+    : browser_context_(browser_context), weak_ptr_factory_(this) {}
 
 ExtensionPrinterHandler::~ExtensionPrinterHandler() {
 }
@@ -274,8 +272,7 @@ void ExtensionPrinterHandler::ConvertToPWGRaster(
       data.get(),
       PWGRasterConverter::GetConversionSettings(printer_description, page_size),
       PWGRasterConverter::GetBitmapSettings(printer_description, ticket),
-      base::Bind(&UpdateJobFileInfo, base::Passed(&job), slow_task_runner_,
-                 callback));
+      base::Bind(&UpdateJobFileInfo, base::Passed(&job), callback));
 }
 
 void ExtensionPrinterHandler::DispatchPrintJob(

chrome/browser/ui/webui/print_preview/extension_printer_handler.h

@@ -19,7 +19,6 @@ namespace base {
 class DictionaryValue;
 class ListValue;
 class RefCountedMemory;
-class TaskRunner;
 }
 
 namespace content {
@@ -49,9 +48,7 @@ class ExtensionPrinterHandler : public PrinterHandler {
   using PrintJobCallback = base::Callback<void(
       std::unique_ptr<extensions::PrinterProviderPrintJob>)>;
 
-  ExtensionPrinterHandler(
-      content::BrowserContext* browser_context,
-      const scoped_refptr<base::TaskRunner>& slow_task_runner);
+  explicit ExtensionPrinterHandler(content::BrowserContext* browser_context);
 
   ~ExtensionPrinterHandler() override;
 
@@ -122,8 +119,6 @@ class ExtensionPrinterHandler : public PrinterHandler {
   std::unique_ptr<printing::PWGRasterConverter> pwg_raster_converter_;
   int pending_enumeration_count_ = 0;
 
-  scoped_refptr<base::TaskRunner> slow_task_runner_;
-
   base::WeakPtrFactory<ExtensionPrinterHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionPrinterHandler);

chrome/browser/ui/webui/print_preview/extension_printer_handler_unittest.cc

@@ -22,7 +22,6 @@
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/values_test_util.h"
-#include "base/threading/thread_task_runner_handle.h"
 #include "base/values.h"
 #include "chrome/browser/extensions/test_extension_environment.h"
 #include "chrome/browser/printing/pwg_raster_converter.h"
@@ -462,8 +461,8 @@ class ExtensionPrinterHandlerTest : public testing::Test {
   void SetUp() override {
     extensions::PrinterProviderAPIFactory::GetInstance()->SetTestingFactory(
         env_.profile(), &BuildTestingPrinterProviderAPI);
-    extension_printer_handler_.reset(new ExtensionPrinterHandler(
-        env_.profile(), base::ThreadTaskRunnerHandle::Get()));
+    extension_printer_handler_.reset(
+        new ExtensionPrinterHandler(env_.profile()));
 
     pwg_raster_converter_ = new FakePWGRasterConverter();
     extension_printer_handler_->SetPWGRasterConverterForTesting(

chrome/browser/ui/webui/print_preview/printer_handler.cc

@@ -4,12 +4,11 @@
 
 #include "chrome/browser/ui/webui/print_preview/printer_handler.h"
 
-#include "base/threading/worker_pool.h"
 #include "chrome/browser/ui/webui/print_preview/extension_printer_handler.h"
 
 // static
 std::unique_ptr<PrinterHandler> PrinterHandler::CreateForExtensionPrinters(
     content::BrowserContext* browser_context) {
-  return std::unique_ptr<ExtensionPrinterHandler>(new ExtensionPrinterHandler(
-      browser_context, base::WorkerPool::GetTaskRunner(true)));
+  return std::unique_ptr<ExtensionPrinterHandler>(
+      new ExtensionPrinterHandler(browser_context));
 }