Scale scrollbar in use-zoom-for-dsf mode

third_party/WebKit/Source/platform/scroll/Scrollbar.cpp

Index: third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp b/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
index a86da068c7f3476ad441ca7d09b13d5428fbc8d4..4d0b700da4bc67f026e3408b4010feb7d3bb4888 100644
--- a/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
+++ b/third_party/WebKit/Source/platform/scroll/Scrollbar.cpp
@@ -26,6 +26,7 @@
 #include "platform/scroll/Scrollbar.h"
 
 #include <algorithm>
+#include "platform/HostWindow.h"
 #include "platform/PlatformGestureEvent.h"
 #include "platform/PlatformMouseEvent.h"
 #include "platform/graphics/paint/CullRect.h"
@@ -40,17 +41,17 @@
 
 namespace blink {
 
-PassRefPtrWillBeRawPtr<Scrollbar> Scrollbar::create(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize size)
+PassRefPtrWillBeRawPtr<Scrollbar> Scrollbar::create(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize size, HostWindow* hostWindow)
 {
-    return adoptRefWillBeNoop(new Scrollbar(scrollableArea, orientation, size));
+    return adoptRefWillBeNoop(new Scrollbar(scrollableArea, orientation, size, hostWindow));
 }
 
 PassRefPtrWillBeRawPtr<Scrollbar> Scrollbar::createForTesting(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize size, ScrollbarTheme* theme)
 {
-    return adoptRefWillBeNoop(new Scrollbar(scrollableArea, orientation, size, theme));
+    return adoptRefWillBeNoop(new Scrollbar(scrollableArea, orientation, size, nullptr, theme));
 }
 
-Scrollbar::Scrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize controlSize, ScrollbarTheme* theme)
+Scrollbar::Scrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orientation, ScrollbarControlSize controlSize, HostWindow* hostWindow, ScrollbarTheme* theme)
     : m_scrollableArea(scrollableArea)
     , m_orientation(orientation)
     , m_controlSize(controlSize)
@@ -78,6 +79,12 @@ Scrollbar::Scrollbar(ScrollableArea* scrollableArea, ScrollbarOrientation orient
     // scrollbar thickness and use it when sizing scrollbars (rather than leaving one dimension of the scrollbar
     // alone when sizing).
     int thickness = m_theme.scrollbarThickness(controlSize);
+    if (hostWindow) {
+        IntRect tmp(0, 0, 100, 0);

[skobes, 2016/01/07 21:49:10]

Where does this "100" come from?

[oshima, 2016/01/09 00:58:39]

It's picked as large enough number so that you can compute the viewport to
window ratio.
I didn't add new method because this serves enough and got lgtm from owner in
the past.
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...


I can add new method if you want, but want to do that in separate CL as it
involves other unrelated changes, and need owners approval.

[skobes, 2016/01/11 03:28:29]

It would be much clearer to have an overload of viewportToScreen that takes a
WebSize, and pass the thickness to it directly.  Separate CL is fine but at
least add a comment here explaining what it's doing.

Related: are the horizontal and vertical ratios always the same?  If not you
will need to use height or width here depending on scrollbar orientation.

[skobes, 2016/01/11 03:30:52]

Clarification: I meant something like HostWindow::viewportToScreen(IntSize&)
delegating to WebWidgetClient::convertViewportToWindow(WebSize&).

+        tmp = hostWindow->viewportToScreen(tmp);
+        thickness *= 100.f / tmp.width();
+    }
+
     Widget::setFrameRect(IntRect(0, 0, thickness, thickness));
 
     m_currentPos = scrollableAreaCurrentPos();