Modifies the threshold for hidpi displays.

ash/display/display_change_observer_chromeos.cc

Index: ash/display/display_change_observer_chromeos.cc
diff --git a/ash/display/display_change_observer_chromeos.cc b/ash/display/display_change_observer_chromeos.cc
index 862b22867097cfa2a44c1927f89caebf8e94c21a..02578e8444c05fd90c8562d73f4a7efa9f484e15 100644
--- a/ash/display/display_change_observer_chromeos.cc
+++ b/ash/display/display_change_observer_chromeos.cc
@@ -34,6 +34,14 @@ namespace {
 // Higher DPI than this will use device_scale_factor=2.
 const unsigned int kHighDensityDPIThreshold = 170;
 
+// The HiDPI threshold for bigger (usually external) monitors. Lower threshold

[oshima, 2014/04/08 20:39:47]

"Large" is probably better term. Can you update the one above to XxxSmall ?

[Jun Mukai, 2014/04/09 20:20:07]

Done.

+// makes sense for bigger monitors, because such monitors should be located
+// farther from the user's face usually. See http://crbug.com/348279
+const unsigned int kHighDensityDPIThresholdBigger = 150;
+
+// The width threshold in mm for "bigger" monitors.
+const int kBiggerDisplayWidthThresholdMM = 500;
+
 // 1 inch in mm.
 const float kInchInMm = 25.4f;
 
@@ -48,6 +56,19 @@ struct DisplayModeSorter {
   }
 };
 
+bool ShouldBeHiDPI(const gfx::Size& physical_size,

[oshima, 2014/04/08 20:39:47]

Can you change this to return scale factor (like GetScaleFactor(...))
and write unit tests?

[Jun Mukai, 2014/04/09 20:20:07]

Done.

+                   const ui::DisplayMode& mode_info) {
+  if (ui::IsDisplaySizeBlackListed(physical_size))
+    return false;
+
+  const unsigned int dpi = (kInchInMm * mode_info.size().width() /
+                            physical_size.width());
+  const unsigned int threshold =
+      (physical_size.width() >= kBiggerDisplayWidthThresholdMM) ?
+      kHighDensityDPIThresholdBigger : kHighDensityDPIThreshold;
+  return dpi > threshold;
+}
+
 }  // namespace
 
 // static
@@ -134,11 +155,9 @@ void DisplayChangeObserver::OnDisplayModeChanged(
       continue;
 
     float device_scale_factor = 1.0f;
-    if (!ui::IsDisplaySizeBlackListed(output.display->physical_size()) &&
-        (kInchInMm * mode_info->size().width() /
-         output.display->physical_size().width()) > kHighDensityDPIThreshold) {
+    if (ShouldBeHiDPI(output.display->physical_size(), *mode_info))
       device_scale_factor = 2.0f;
-    }
+
     gfx::Rect display_bounds(output.display->origin(), mode_info->size());
 
     std::vector<DisplayMode> display_modes = GetDisplayModeList(output);