Make new TaskRunner, SequencedTaskRunner, and SingleThreadTaskRunner interfaces

base/base.gypi

Index: base/base.gypi
diff --git a/base/base.gypi b/base/base.gypi
index 2d10270ab212fdc2f8bccc2dafc7f55355a959d7..76993533eb956e9da244380ff3be3767ed024569 100644
--- a/base/base.gypi
+++ b/base/base.gypi
@@ -95,6 +95,9 @@
           'eintr_wrapper.h',
           'environment.cc',
           'environment.h',
+          'executor.cc',
+          'executor.h',
+          'executor_helpers.h',
           'file_descriptor_posix.h',
           'file_path.cc',
           'file_path.h',
@@ -187,6 +190,7 @@
           'memory/weak_ptr.h',
           'message_loop.cc',
           'message_loop.h',
+          'message_loop_helpers.h',
           'message_loop_proxy.cc',
           'message_loop_proxy.h',
           'message_loop_proxy_impl.cc',
@@ -252,6 +256,7 @@
           'scoped_native_library.h',
           'scoped_temp_dir.cc',
           'scoped_temp_dir.h',
+          'serial_executor.h',
           'sha1.h',
           'sha1_portable.cc',
           'sha1_win.cc',
@@ -259,6 +264,7 @@
           'shared_memory_android.cc',
           'shared_memory_posix.cc',
           'shared_memory_win.cc',
+          'single_thread_executor.h',
           'spin_wait.h',
           'stack_container.h',
           'stl_util.h',