Store rotation/ui scale to local state.

ash/display/display_info.cc

Index: ash/display/display_info.cc
diff --git a/ash/display/display_info.cc b/ash/display/display_info.cc
index b46dceb12490548732c61498bf512cbd27262bbd..1e105df30f6ca34e28ba7300814d46847091770a 100644
--- a/ash/display/display_info.cc
+++ b/ash/display/display_info.cc
@@ -138,8 +138,21 @@ void DisplayInfo::CopyFromNative(const DisplayInfo& native_info) {
   bounds_in_pixel_ = native_info.bounds_in_pixel_;
   size_in_pixel_ = native_info.size_in_pixel_;
   device_scale_factor_ = native_info.device_scale_factor_;
-  rotation_ = native_info.rotation_;
-  ui_scale_ = native_info.ui_scale_;
+
+  // Rotation_ and ui_scale_ are given by preference, or unit
+  // tests. Don't copy if this native_info came from
+  // DisplayChangeObserverX11.
+  if (native_info.ui_scale() >= 1.0f) {
+    rotation_ = native_info.rotation_;
+    ui_scale_ = native_info.ui_scale_;
+  }
+  // It makes little sense to scale beyond the original
+  // resolution. This guard is to protect applying
+  // ui_scale to an external display whose DPI has changed
+  // from 2.0 to 1.0 for some reason.
+  if (ui_scale_ > device_scale_factor_)
+    ui_scale_ = 1.0f;
+
   // Don't copy insets as it may be given by preference.  |rotation_|
   // is treated as a native so that it can be specified in
   // |CreateFromSpec|.