Reland Change minimum length of Aura overlay scrollbars.

content/child/webthemeengine_impl_android.cc

Index: content/child/webthemeengine_impl_android.cc
diff --git a/content/child/webthemeengine_impl_android.cc b/content/child/webthemeengine_impl_android.cc
index fa693b3cf9cb828de50d999ba530dc43c3a85629..d659241610153438bf17cbc3dbe73d0a3699d3de 100644
--- a/content/child/webthemeengine_impl_android.cc
+++ b/content/child/webthemeengine_impl_android.cc
@@ -39,13 +39,15 @@ static ui::NativeTheme::Part NativeThemePart(WebThemeEngine::Part part) {
     case WebThemeEngine::PartScrollbarUpArrow:
       return ui::NativeTheme::kScrollbarUpArrow;
     case WebThemeEngine::PartScrollbarHorizontalThumb:
+      return ui::NativeTheme::kScrollbarHorizontalThumb;
     case WebThemeEngine::PartScrollbarVerticalThumb:
+      return ui::NativeTheme::kScrollbarVerticalThumb;
     case WebThemeEngine::PartScrollbarHorizontalTrack:
+      return ui::NativeTheme::kScrollbarHorizontalTrack;
     case WebThemeEngine::PartScrollbarVerticalTrack:
+      return ui::NativeTheme::kScrollbarVerticalTrack;
     case WebThemeEngine::PartScrollbarCorner:
-      // Android doesn't draw scrollbars.
-      NOTREACHED();
-      return static_cast<ui::NativeTheme::Part>(0);
+      return ui::NativeTheme::kScrollbarCorner;
     case WebThemeEngine::PartCheckbox:
       return ui::NativeTheme::kCheckbox;
     case WebThemeEngine::PartRadio:
@@ -167,9 +169,21 @@ static void GetNativeThemeExtraParams(
 }
 
 blink::WebSize WebThemeEngineImpl::getSize(WebThemeEngine::Part part) {
-  ui::NativeTheme::ExtraParams extra;
-  return ui::NativeTheme::GetInstanceForWeb()->GetPartSize(
-      NativeThemePart(part), ui::NativeTheme::kNormal, extra);
+  switch (part) {
+    case ui::NativeTheme::kScrollbarHorizontalThumb:
+    case ui::NativeTheme::kScrollbarVerticalThumb: {
+      // Minimum length for scrollbar thumb is the scrollbar thickness.
+      ScrollbarStyle style;
+      getOverlayScrollbarStyle(&style);
+      int scrollbarThickness = style.thumbThickness + style.scrollbarMargin;
+      return gfx::Size(scrollbarThickness, scrollbarThickness);
+    }
+    default: {
+      ui::NativeTheme::ExtraParams extra;
+      return ui::NativeTheme::GetInstanceForWeb()->GetPartSize(
+          NativeThemePart(part), ui::NativeTheme::kNormal, extra);
+    }
+  }
 }
 
 void WebThemeEngineImpl::getOverlayScrollbarStyle(ScrollbarStyle* style) {