Use list instead of pair to represent the set of displays.

ash/shelf/shelf_layout_manager.cc

Index: ash/shelf/shelf_layout_manager.cc
diff --git a/ash/shelf/shelf_layout_manager.cc b/ash/shelf/shelf_layout_manager.cc
index aae4793cffb419036f10dd6c65a5bdc5a89496f1..5b76b1f66376c0d7071a51bc2c83a8319f5d87bb 100644
--- a/ash/shelf/shelf_layout_manager.cc
+++ b/ash/shelf/shelf_layout_manager.cc
@@ -705,6 +705,12 @@ void ShelfLayoutManager::UpdateBoundsAndOpacity(
                         target_bounds.shelf_bounds_in_root.x());
     status_bounds.set_y(status_bounds.y() +
                         target_bounds.shelf_bounds_in_root.y());
+    LOG(ERROR) << "Status Area Widget Bounds:"

[msw, 2016/02/02 22:54:10]

Did you mean to land this? It's spamming logs, like this:
https://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20ChromeOS%20...

+               << ScreenUtil::ConvertRectToScreen(
+                      shelf_->status_area_widget()->GetNativeView()->parent(),
+                      status_bounds)
+                      .ToString();
+
     shelf_->status_area_widget()->SetBounds(
         ScreenUtil::ConvertRectToScreen(
             shelf_->status_area_widget()->GetNativeView()->parent(),