Run parsing JSON into ResourceList on blocking pool.

This CL moves the parsing JSON task from UI thread to blocking pool.
Along the change, thin struct OnParseResourceListCompletedParams is introduced
for memory management and adapt callback arguments.

BUG=165088
TEST=Ran unit_tests and chromeos_unittests.


Review URL: https://chromiumcodereview.appspot.com/11783025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175793 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chromeos/drive/drive_api_service.cc

@@ -9,6 +9,8 @@
 
 #include "base/bind.h"
 #include "base/message_loop_proxy.h"
+#include "base/task_runner_util.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
 #include "chrome/browser/google_apis/drive_api_operations.h"
 #include "chrome/browser/google_apis/drive_api_parser.h"
@@ -30,35 +32,62 @@ const char kDriveScope[] = "https://www.googleapis.com/auth/drive";
 const char kDriveAppsReadonlyScope[] =
     "https://www.googleapis.com/auth/drive.apps.readonly";
 
-// Parses the JSON value into ResourceList and runs |callback|.
-void ParseResourceListAndRun(
-    const google_apis::GetResourceListCallback& callback,
-    google_apis::GDataErrorCode error,
-    scoped_ptr<base::Value> value) {
+scoped_ptr<google_apis::ResourceList> ParseResourceListOnBlockingPool(
+    scoped_ptr<base::Value> value, google_apis::GDataErrorCode* error) {
   if (!value) {
-    callback.Run(error, scoped_ptr<google_apis::ResourceList>());
-    return;
+    // JSON value is not available.
+    return scoped_ptr<google_apis::ResourceList>();
   }
 
-  // TODO(satorux): Parse the JSON value on a blocking pool. crbug.com/165088
+  // Parse the value into ResourceList via ChangeList.
+  // If failed, set (i.e. overwrite) the error flag and return immediately.
   scoped_ptr<google_apis::ChangeList> change_list(
       google_apis::ChangeList::CreateFrom(*value));
   if (!change_list) {
-    callback.Run(google_apis::GDATA_PARSE_ERROR,
-                 scoped_ptr<google_apis::ResourceList>());
-    return;
+    *error = google_apis::GDATA_PARSE_ERROR;
+    return scoped_ptr<google_apis::ResourceList>();
   }
 
-  // TODO(satorux): Do the conversion on a blocking pool too. crbug.com/165088
   scoped_ptr<google_apis::ResourceList> resource_list =
       google_apis::ResourceList::CreateFromChangeList(*change_list);
   if (!resource_list) {
-    callback.Run(google_apis::GDATA_PARSE_ERROR,
-                 scoped_ptr<google_apis::ResourceList>());
-    return;
+    *error = google_apis::GDATA_PARSE_ERROR;
+    return scoped_ptr<google_apis::ResourceList>();
   }
 
-  callback.Run(error, resource_list.Pass());
+  // Pass the result to the params, so that DidParseResourceListOnBlockingPool
+  // defined below can process it.
+  return resource_list.Pass();
+}
+
+// Callback invoked when the parsing of resource list is completed,
+// regardless whether it is succeeded or not.
+void DidParseResourceListOnBlockingPool(
+    const google_apis::GetResourceListCallback& callback,
+    google_apis::GDataErrorCode* error,
+    scoped_ptr<google_apis::ResourceList> resource_list) {
+  callback.Run(*error, resource_list.Pass());
+}
+
+// Sends a task to parse the JSON value into ResourceList on blocking pool,
+// with a callback which is called when the task is done.
+void ParseResourceListOnBlockingPoolAndRun(
+    const google_apis::GetResourceListCallback& callback,
+    google_apis::GDataErrorCode in_error,
+    scoped_ptr<base::Value> value) {
+  // Note that the error value may be overwritten in
+  // ParseResoruceListOnBlockingPool before used in
+  // DidParseResourceListOnBlockingPool.
+  google_apis::GDataErrorCode* error =
+      new google_apis::GDataErrorCode(in_error);
+
+  PostTaskAndReplyWithResult(
+      BrowserThread::GetBlockingPool(),
+      FROM_HERE,
+      base::Bind(&ParseResourceListOnBlockingPool,
+                 base::Passed(&value), error),
+      base::Bind(&DidParseResourceListOnBlockingPool,
+                 callback, base::Owned(error)));
 }
 
 // Parses the JSON value to ResourceEntry runs |callback|.
@@ -223,7 +252,7 @@ void DriveAPIService::GetFilelist(
           url_generator_,
           url,
           search_query,
-          base::Bind(&ParseResourceListAndRun, callback)));
+          base::Bind(&ParseResourceListOnBlockingPoolAndRun, callback)));
 }
 
 void DriveAPIService::GetChangelist(
@@ -240,7 +269,7 @@ void DriveAPIService::GetChangelist(
           url_generator_,
           url,
           start_changestamp,
-          base::Bind(&ParseResourceListAndRun, callback)));
+          base::Bind(&ParseResourceListOnBlockingPoolAndRun, callback)));
 }
 
 void DriveAPIService::GetResourceEntry(