Convert base::Bind -> base::Bind{Once,Repeating} in ThemeService

base::Bind is deprecated and should be replaced with more explicit
calls. ThemeService only has a single use, which can be converted to the
preferred BindOnce.

Bug: 1007635
Change-Id: I83d7af39bbf6be73262c024972df6b3652574e19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487840Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Alex Turner <alexmt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819037}

PRESUBMIT.py

@@ -367,7 +367,6 @@ _NOT_CONVERTED_TO_MODERN_BIND_AND_CALLBACK = '|'.join((
   '^chrome/browser/supervised_user/',
   '^chrome/browser/sync_file_system/',
   '^chrome/browser/sync/',
-  '^chrome/browser/themes/theme_service.cc',
   '^chrome/browser/thumbnail/cc/',
   '^chrome/browser/translate/',
   '^chrome/browser/ui/',

chrome/browser/themes/theme_service.cc

@@ -278,8 +278,8 @@ void ThemeService::Init() {
   theme_observer_ = std::make_unique<ThemeObserver>(this);
 
   extensions::ExtensionSystem::Get(profile_)->ready().Post(
-      FROM_HERE, base::Bind(&ThemeService::OnExtensionServiceReady,
-                            weak_ptr_factory_.GetWeakPtr()));
+      FROM_HERE, base::BindOnce(&ThemeService::OnExtensionServiceReady,
+                                weak_ptr_factory_.GetWeakPtr()));
 #endif
   theme_syncable_service_.reset(new ThemeSyncableService(profile_, this));