Add Get/SetDisplayLayout to chrome.system.display extension API

extensions/common/api/system_display.idl

Index: extensions/common/api/system_display.idl
diff --git a/extensions/common/api/system_display.idl b/extensions/common/api/system_display.idl
index 31fe79c6e97ae7522f0578a9d999d9453f14652b..bc022d8f6588698d1a82b49dac3eb70a699d8a1c 100644
--- a/extensions/common/api/system_display.idl
+++ b/extensions/common/api/system_display.idl
@@ -59,6 +59,25 @@ namespace system.display {
     boolean isSelected;
   };
 
+  // Layout position, i.e. edge of parent that the display is attached to.
+  enum LayoutPosition { top, right, bottom, left };
+
+  dictionary DisplayLayout {
+    // The unique identifier of the display.
+    DOMString id;
+
+    // The unique identifier of the parent display. Empty if this is the root.
+    DOMString parentId;
+
+    // The layout position of this display relative to the parent. This will
+    // be ignored for the root.
+    LayoutPosition position;
+
+    // The offset of the display along the connected edge. 0 indicates that
+    // the topmost or leftmost corners are aligned.
+    long offset;
+  };
+
   dictionary DisplayUnitInfo {
     // The unique identifier of the display.
     DOMString id;
@@ -152,12 +171,17 @@ namespace system.display {
   };
 
   callback DisplayInfoCallback = void (DisplayUnitInfo[] displayInfo);
+  callback DisplayLayoutCallback = void (DisplayLayout[] layouts);
   callback SetDisplayUnitInfoCallback = void();
 
   interface Functions {
     // Get the information of all attached display devices.
     static void getInfo(DisplayInfoCallback callback);
 
+    // Get the layout info for all displays.
+    // NOTE: This is only available to Chrome OS Kiosk apps and Web UI.
+    static void getDisplayLayout(DisplayLayoutCallback callback);
+
     // Updates the properties for the display specified by |id|, according to
     // the information provided in |info|. On failure, $(ref:runtime.lastError)
     // will be set.
@@ -174,6 +198,12 @@ namespace system.display {
         DisplayProperties info,
         optional SetDisplayUnitInfoCallback callback);
 
+    // Set the layout for all displays. Any display not included will use the
+    // default layout. If a layout would overlap or be otherwise invalid it
+    // will be adjusted to a valid layout. After layout is resolved, an
+    // onDisplayChanged event will be triggered.
+    static void setDisplayLayout(DisplayLayout[] layouts);

[asargent_no_longer_on_chrome, 2016/06/16 19:08:30]

optional: you might consider adding a callback which reports back whether the
layouts passed were used successfully or had to be adjusted. Callers can likely
figure that out themselves by listening for the onDisplayChanged, but doing so
might be a bit more cumbersome than if you just told them directly.

[stevenjb, 2016/06/17 01:34:59]

I don't want to add too much complexity to the API in anticipation of usage that
will probably never exist, but this should at least call a void callback when
done so that the error state can be queried, same as with setDisplayProperties.
Done.

+
     // Enables/disables the unified desktop feature. Note that this simply
     // enables the feature, but will not change the actual desktop mode.
     // (That is, if the desktop is in mirror mode, it will stay in mirror mode)