Allow base callbacks everywhere in Blink.

We are now mostly ready to start replacing WTF::Function with
base callbacks. This patch updates DEPS and audit-non-blink-usage.py so
we can use base callback stuff in Blink.

Bug: 771087, 763980
Change-Id: I8b41ab2c3e9e72279039685960b6dd1b558ee457
Reviewed-on: https://chromium-review.googlesource.com/807754Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522367}

third_party/WebKit/Source/DEPS

 include_rules = [
+    "+base/callback.h",
+    "+base/callback_forward.h",
     "+base/debug",
     "+base/macros.h",
     "+base/memory/weak_ptr.h",

third_party/WebKit/Source/platform/DEPS

@@ -4,8 +4,6 @@ include_rules = [
     "+base/allocator/partition_allocator/oom.h",
     "+base/bind.h",
     "+base/bind_helpers.h",
-    "+base/callback.h",
-    "+base/callback_forward.h",
     "+base/feature_list.h",
     "+base/files",
     "+base/guid.h",

third_party/WebKit/Tools/Scripts/audit-non-blink-usage.py

@@ -43,6 +43,13 @@ _CONFIG = [
             'base::span',
             'logging::GetVlogLevel',
 
+            # //base/callback.h is allowed, but you need to use WTF::Bind or
+            # WTF::BindRepeating to create callbacks in Blink.
+            'base::OnceCallback',
+            'base::OnceClosure',
+            'base::RepeatingCallback',
+            'base::RepeatingClosure',
+
             # Debugging helpers from //base/debug are allowed everywhere.
             'base::debug::.+',