TaskScheduler: Remove base::ExecutionMode.

base/task_scheduler/task_traits.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_TRAITS_H_
 #define BASE_TASK_SCHEDULER_TASK_TRAITS_H_
 
 #include <stdint.h>
 
 #include <iosfwd>
@@ skipping 95 matching lines @@
 
   // Returns the shutdown behavior of tasks with these traits.
   TaskShutdownBehavior shutdown_behavior() const { return shutdown_behavior_; }
 
  private:
   bool with_file_io_;
   TaskPriority priority_;
   TaskShutdownBehavior shutdown_behavior_;
 };
 
-// Describes how tasks are executed by a task runner.
-enum class ExecutionMode {
-  // Can execute multiple tasks at a time in any order.
-  PARALLEL,
-
-  // Executes one task at a time in posting order. The sequence’s priority is
-  // equivalent to the highest priority pending task in the sequence.
-  SEQUENCED,
-
-  // Executes one task at a time on a single thread in posting order.
-  SINGLE_THREADED,
-};
-
 // Returns string literals for the enums defined in this file. These methods
 // should only be used for tracing and debugging.
 BASE_EXPORT const char* TaskPriorityToString(TaskPriority task_priority);
 BASE_EXPORT const char* TaskShutdownBehaviorToString(
     TaskShutdownBehavior task_priority);
-BASE_EXPORT const char* ExecutionModeToString(ExecutionMode task_priority);
 
 // Stream operators so that the enums defined in this file can be used in
 // DCHECK and EXPECT statements.
 BASE_EXPORT std::ostream& operator<<(std::ostream& os,
                                      const TaskPriority& shutdown_behavior);
 BASE_EXPORT std::ostream& operator<<(
     std::ostream& os,
     const TaskShutdownBehavior& shutdown_behavior);
-BASE_EXPORT std::ostream& operator<<(std::ostream& os,
-                                     const ExecutionMode& execution_mode);
 
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_TRAITS_H_