Fix code around display overscan settings.

ash/display/multi_display_manager.cc

Index: ash/display/multi_display_manager.cc
diff --git a/ash/display/multi_display_manager.cc b/ash/display/multi_display_manager.cc
index aba85f02e5af38321ebd2485eeec50d0a70b6d03..ef71b50d261a3b56243621cc3f8aee82dd93f160 100644
--- a/ash/display/multi_display_manager.cc
+++ b/ash/display/multi_display_manager.cc
@@ -148,6 +148,22 @@ const gfx::Display& MultiDisplayManager::FindDisplayContainingPoint(
 
 void MultiDisplayManager::SetOverscanInsets(int64 display_id,
                                             const gfx::Insets& insets_in_dip) {
+  std::map<int64, gfx::Insets>::const_iterator old_overscan =
+      overscan_mapping_.find(display_id);
+  if (old_overscan != overscan_mapping_.end()) {
+    gfx::Insets old_insets = old_overscan->second;
+    for (DisplayList::iterator iter = displays_.begin();

[oshima, 2012/10/16 23:54:17]

FindDisplayForId

[Jun Mukai, 2012/10/17 00:07:49]

Thanks.  But as far as I see, it returns a const reference, so the code to
reimburse the existing insets could be awkward -- I want to edit an existing
display in the list.  Also it raises DLOG(FATAL) in case no displays are found,
but it wouldn't be exceptional here.

By the way, I found GetDisplayForId() too, and both are almost identical.  Why
do we have both?

[oshima, 2012/10/17 01:09:40]

FindDisplayId returns non const reference. GetDisplayId is const versino of it.
I think it's just mistake that const/non const versions have different name and
one of them should be renamed. (it'd be outside of this scope)

[Jun Mukai, 2012/10/17 15:45:46]

Done.

+         iter != displays_.end(); ++iter) {
+      if (iter->id() == display_id) {
+        // Reimburse the existing insets before applying the new insets.
+        gfx::Rect bounds = iter->bounds_in_pixel();
+        gfx::Insets negated_insets = old_insets.Scale(-1);
+        bounds.Inset(negated_insets.Scale(iter->device_scale_factor()));

[oshima, 2012/10/16 23:54:17]

Scale(- iter->device_scale_factor()); (or -1 *)

[Jun Mukai, 2012/10/17 00:07:49]

Done.

+        iter->SetScaleAndBounds(iter->device_scale_factor(), bounds);
+        break;
+      }
+    }
+  }
   overscan_mapping_[display_id] = insets_in_dip;
   OnNativeDisplaysChanged(displays_);
 }