Replace hide-scrollbars flag with a web setting.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index f3710f0d20314c96e033feab385d84e7201682cc..6d015c29b0a3eaf90876db5e5937bd045f49b0b4 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1051,6 +1051,9 @@ void PaintLayerScrollableArea::setHasHorizontalScrollbar(bool hasScrollbar)
     if (FreezeScrollbarsScope::scrollbarsAreFrozen())
         return;
 
+    if (box().frame()->settings() && box().frame()->settings()->hideScrollbars())

[dcheng, 2016/09/19 10:04:47]

Is this null check of settings() required? We do call this during document
shutdown, but at that point, I think the Settings object should still be
non-null.

[skobes, 2016/09/19 18:37:22]

The question is whether Frame::m_host can ever be null at this point.  I am not
quite sure, but we do these checks in a lot of places and Frame::settings() has
the comment "can be null".

[skobes, 2016/09/19 19:31:20]

Ok, let's change the null checks to DCHECKs.

[Eric Seckler, 2016/09/22 12:41:56]

Done. I also changed this in FrameView, assuming it's the same reasoning there.
Does that make sense?

+        hasScrollbar = false;
+
     if (hasScrollbar == hasHorizontalScrollbar())
         return;
 
@@ -1078,6 +1081,9 @@ void PaintLayerScrollableArea::setHasVerticalScrollbar(bool hasScrollbar)
     if (FreezeScrollbarsScope::scrollbarsAreFrozen())
         return;
 
+    if (box().frame()->settings() && box().frame()->settings()->hideScrollbars())
+        hasScrollbar = false;
+
     if (hasScrollbar == hasVerticalScrollbar())
         return;