Avoid calling the GetSystemMetrics API in the renderer process on Windows to get the scrollbar metr…

content/child/webthemeengine_impl_default.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/child/webthemeengine_impl_default.h"
+#include "content/public/common/renderer_preferences.h"
 
 #include "skia/ext/platform_canvas.h"
 #include "third_party/WebKit/public/platform/WebRect.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
 #include "ui/native_theme/native_theme.h"
 
 using blink::WebCanvas;
 using blink::WebColor;
 using blink::WebRect;
 using blink::WebThemeEngine;
@@ skipping 137 matching lines @@
       native_theme_extra_params->progress_bar.value_rect_width =
           extra_params->progressBar.valueRectWidth;
       native_theme_extra_params->progress_bar.value_rect_height =
           extra_params->progressBar.valueRectHeight;
       break;
     default:
       break;  // Parts that have no extra params get here.
   }
 }
 
+int32 WebThemeEngineImpl::vertical_scroll_bar_width_ = 0;
+int32 WebThemeEngineImpl::horizontal_scroll_bar_height_ = 0;

[brucedawson, 2015/04/03 17:00:24]

I can't see anywhere where this variable (or the two *arrow_bitmap_* variables)
are read from. It looks like we only need to cache SM_CXVSCROLL, I think?

[ananta, 2015/04/03 19:17:03]

Caching them on an if needed basis.

+int32 WebThemeEngineImpl::vertical_arrow_bitmap_height_ = 0;
+int32 WebThemeEngineImpl::horizontal_arrow_bitmap_width_ = 0;
+
 blink::WebSize WebThemeEngineImpl::getSize(WebThemeEngine::Part part) {
   ui::NativeTheme::ExtraParams extra;
-  return ui::NativeTheme::instance()->GetPartSize(NativeThemePart(part),
-                                                   ui::NativeTheme::kNormal,
-                                                   extra);
+  ui::NativeTheme::Part native_theme_part = NativeThemePart(part);
+#if defined(OS_WIN)
+  switch (native_theme_part) {
+    case ui::NativeTheme::kScrollbarDownArrow:
+    case ui::NativeTheme::kScrollbarLeftArrow:
+    case ui::NativeTheme::kScrollbarRightArrow:
+    case ui::NativeTheme::kScrollbarUpArrow:
+    case ui::NativeTheme::kScrollbarHorizontalThumb:
+    case ui::NativeTheme::kScrollbarVerticalThumb:
+    case ui::NativeTheme::kScrollbarHorizontalTrack:
+    case ui::NativeTheme::kScrollbarVerticalTrack: {
+      // If we have the scrollbar width cached return it.
+      if (WebThemeEngineImpl::vertical_scroll_bar_width_) {

[brucedawson, 2015/04/03 17:00:24]

When would we not have the scrollbar width cached? Or should we replicate the
"if (size == 0) size = 17;" logic here (from native_theme_win.cc)?

[ananta, 2015/04/03 19:17:04]

Removed the check. The metrics default to 17

+        return gfx::Size(WebThemeEngineImpl::vertical_scroll_bar_width_,
+                         WebThemeEngineImpl::vertical_scroll_bar_width_);
+      }
+      break;
+    }
+
+    default:
+      break;
+  }
+#endif
+  return ui::NativeTheme::instance()->GetPartSize(native_theme_part,
+                                                  ui::NativeTheme::kNormal,
+                                                  extra);
 }
 
 void WebThemeEngineImpl::paint(
     blink::WebCanvas* canvas,
     WebThemeEngine::Part part,
     WebThemeEngine::State state,
     const blink::WebRect& rect,
     const WebThemeEngine::ExtraParams* extra_params) {
   ui::NativeTheme::ExtraParams native_theme_extra_params;
   GetNativeThemeExtraParams(
@@ skipping 14 matching lines @@
                                               const blink::WebRect& rect) {
   ui::NativeTheme::instance()->PaintStateTransition(
       canvas,
       NativeThemePart(part),
       NativeThemeState(startState),
       NativeThemeState(endState),
       progress,
       gfx::Rect(rect));
 }
 
+// static
+void WebThemeEngineImpl::SetVerticalScrollbarWidth(
+    int32 vertical_scroll_bar_width) {
+  vertical_scroll_bar_width_ = vertical_scroll_bar_width;
+}
+
+// static
+void WebThemeEngineImpl::SetHorizontalScrollbarHeight(
+    int32 horizontal_scroll_bar_height) {
+  horizontal_scroll_bar_height_ = horizontal_scroll_bar_height;
+}
+
+// static
+void WebThemeEngineImpl::SetVerticalArrowBitmapHeight(
+    int32 vertical_arrow_bitmap_height) {
+  vertical_arrow_bitmap_height_ = vertical_arrow_bitmap_height;
+}
+
+// static
+void WebThemeEngineImpl::SetHorizontalArrowBitmapWidth(
+    int32 horizontal_arrow_bitmap_width) {
+  horizontal_arrow_bitmap_width_ = horizontal_arrow_bitmap_width;
+}
+
 }  // namespace content