[message_loop] Remove message_loop_forward.h

As a final step, replace all includes back:
- mv message_loop_current.h message_loop.h
- s/message_loop_forward.h/message_loop.h/ in all includes.
- s/message_loop_forward.h/message_loop.h/ in base/BUILD.gn
- Remove message_loop_forward.h from third_party/DEPS.

[email protected]
[email protected]
BUG=891670

Change-Id: I623077025701459ddb7045cbcfdad138aa90a9e4
Reviewed-on: https://chromium-review.googlesource.com/c/1313110
Reviewed-by: Alexander Timin <[email protected]>
Reviewed-by: Gabriel Charette <[email protected]>
Cr-Commit-Position: refs/heads/master@{#604690}
diff --git a/gpu/angle_end2end_tests_main.cc b/gpu/angle_end2end_tests_main.cc
index bb24e92..cb2c65e 100644
--- a/gpu/angle_end2end_tests_main.cc
+++ b/gpu/angle_end2end_tests_main.cc
@@ -4,7 +4,7 @@
 
 #include "base/bind.h"
 #include "base/command_line.h"
-#include "base/message_loop/message_loop_forward.h"
+#include "base/message_loop/message_loop.h"
 #include "base/test/launcher/unit_test_launcher.h"
 #include "base/test/test_suite.h"
 #include "testing/gmock/include/gmock/gmock.h"