IWYU: ThemeService requires NativeTheme

As ThemeService referes to NativeTheme through a ScopedObserver,
the full declaration is required.

This is also a good opportunity to remove unneeded includes.

Bug: 819294
Change-Id: I9d5bd2e87cfaa76e87f9b5509daea24848906a63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645362
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: José Dapena Paz <jose.dapena@lge.com>
Cr-Commit-Position: refs/heads/master@{#670980}
diff --git a/chrome/browser/themes/theme_service.cc b/chrome/browser/themes/theme_service.cc
index 3069497..fdb21f9 100644
--- a/chrome/browser/themes/theme_service.cc
+++ b/chrome/browser/themes/theme_service.cc
@@ -54,7 +54,6 @@
 #include "ui/gfx/color_palette.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/native_theme/common_theme.h"
-#include "ui/native_theme/native_theme.h"
 
 #if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "base/scoped_observer.h"
diff --git a/chrome/browser/themes/theme_service.h b/chrome/browser/themes/theme_service.h
index 13c0f863..103f83f 100644
--- a/chrome/browser/themes/theme_service.h
+++ b/chrome/browser/themes/theme_service.h
@@ -7,9 +7,7 @@
 
 #include <map>
 #include <memory>
-#include <set>
 #include <string>
-#include <utility>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
@@ -25,6 +23,7 @@
 #include "extensions/buildflags/buildflags.h"
 #include "extensions/common/extension_id.h"
 #include "ui/base/theme_provider.h"
+#include "ui/native_theme/native_theme.h"
 #include "ui/native_theme/native_theme_observer.h"
 
 class BrowserThemePack;