Add ability to create solid color scrollbars in ScrollingCoordinator.

Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.cpp b/Source/core/page/scrolling/ScrollingCoordinator.cpp
index 68a4ddd5b6043e67311961ce598f018fdc64ee0a..cd69b4f1faf26d4cde158280239ff10f89640ae3 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -34,6 +34,7 @@
 #include "core/page/Frame.h"
 #include "core/page/FrameView.h"
 #include "core/page/Page.h"
+#include "core/page/Settings.h"
 #include "core/platform/PlatformWheelEvent.h"
 #include "core/platform/ScrollAnimator.h"
 #include "core/platform/ScrollbarTheme.h"
@@ -208,6 +209,13 @@ static PassOwnPtr<WebScrollbarLayer> createScrollbarLayer(Scrollbar* scrollbar)
     return scrollbarLayer.release();
 }
 
+PassOwnPtr<WebScrollbarLayer> ScrollingCoordinator::createSolidColorScrollbarLayer(ScrollbarOrientation orientation, int thumbThickness)
+{
+    WebKit::WebScrollbar::Orientation webOrientation = (orientation == HorizontalScrollbar) ? WebKit::WebScrollbar::Horizontal : WebKit::WebScrollbar::Vertical;
+    OwnPtr<WebScrollbarLayer> scrollbarLayer = adoptPtr(WebKit::Platform::current()->compositorSupport()->createSolidColorScrollbarLayer(webOrientation, thumbThickness));
+    return scrollbarLayer.release();
+}
+
 static void detachScrollbarLayer(GraphicsLayer* scrollbarGraphicsLayer)
 {
     ASSERT(scrollbarGraphicsLayer);
@@ -271,8 +279,17 @@ void ScrollingCoordinator::scrollableAreaScrollbarLayerDidChange(ScrollableArea*
         }
 
         WebScrollbarLayer* scrollbarLayer = getWebScrollbarLayer(scrollableArea, orientation);
-        if (!scrollbarLayer)
-            scrollbarLayer = addWebScrollbarLayer(scrollableArea, orientation, createScrollbarLayer(scrollbar));
+        if (!scrollbarLayer) {
+            Settings* settings = m_page->mainFrame()->document()->settings();
+            bool shouldCreateSolidColorScrollbar = settings->useSolidColorScrollbars() && settings->usesOverlayScrollbars();

[jamesr, 2013/09/03 23:06:19]

why are you checking usesSolidColor... *and* usesOverlay?  When would
usesSolidColor..() be true but not usesOverlay..()?

[enne (OOO), 2013/09/03 23:47:33]

My thought was that Android would set both of these flags.  Are you suggesting
you'd prefer just checking solid color (and ASSERTing overlay, maybe)?

[wjmaclean, 2013/09/04 13:27:59]

I can confirm that Android does currently set both of these flags. That being
said, it's also reasonable that if the solid color scrollbar setting is true,
then overlay scrollbars should also be true, since the solid color scrollbars
don't do any drawing outside the thumb. So, we could check for
useSolidColorScrollbars() and assert usesOverlayScrollbars().

Let me know which is preferred.

[jamesr, 2013/09/04 20:41:17]

I think either would be fine - either say that one setting requires the other
and ASSERT() or only check the useSolidColorScrollbars() setting and assume the
embedder has set up the settings in a reasonable way.  Let's just pick one.

+
+            OwnPtr<WebScrollbarLayer> webScrollbarLayer;
+            if (shouldCreateSolidColorScrollbar)
+                webScrollbarLayer = createSolidColorScrollbarLayer(orientation, -1);
+            else
+                webScrollbarLayer = createScrollbarLayer(scrollbar);
+            addWebScrollbarLayer(scrollableArea, orientation, webScrollbarLayer.release());
+        }
 
         // Root layer non-overlay scrollbars should be marked opaque to disable
         // blending.