Make window.scroll properties relative to the layout viewport.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 892e73a2ceef5e9090c0867ab8b3fbb0ada8c6c8..dc877122fcf4d3249ee6a6b2915e49f8a0528e8a 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1535,6 +1535,11 @@ const Experiment kExperiments[] = {
      IDS_FLAGS_DISABLE_THREADED_SCROLLING_DESCRIPTION,
      kOsWin | kOsLinux | kOsCrOS | kOsAndroid | kOsMac,
      SINGLE_VALUE_TYPE(switches::kDisableThreadedScrolling)},
+    {"inert-visual-viewport",
+     IDS_FLAGS_INERT_VISUAL_VIEWPORT_NAME,
+     IDS_FLAGS_INERT_VISUAL_VIEWPORT_DESCRIPTION,
+     kOsAll,
+     SINGLE_VALUE_TYPE(switches::kInertVisualViewport)},
     {"bleeding-edge-renderer-mode",
      IDS_FLAGS_BLEEDING_RENDERER_NAME,
      IDS_FLAGS_BLEEDING_RENDERER_DESCRIPTION,