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

content/child/webthemeengine_impl_default.cc

Index: content/child/webthemeengine_impl_default.cc
diff --git a/content/child/webthemeengine_impl_default.cc b/content/child/webthemeengine_impl_default.cc
index 4f78f1c9da21206899fe0e4d18a6d3d087657279..e510e5f93dac47c6eccb753002748434261d11f1 100644
--- a/content/child/webthemeengine_impl_default.cc
+++ b/content/child/webthemeengine_impl_default.cc
@@ -3,6 +3,7 @@
 // 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"
@@ -160,11 +161,39 @@ static void GetNativeThemeExtraParams(
   }
 }
 
+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(
@@ -199,4 +228,28 @@ void WebThemeEngineImpl::paintStateTransition(blink::WebCanvas* canvas,
       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