Add Accessibility Object Model to content features, and add a browser test.

third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt

Index: third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
diff --git a/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt b/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
index a87701ae22b4c3b34744da278312c8a8fad4d3e0..f898d02b094799710ee81ae4228cc3b32dfee66f 100644
--- a/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
+++ b/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
@@ -14,37 +14,6 @@ interface Accelerometer : Sensor
     getter y
     getter z
     method constructor
-interface AccessibleNode
-    attribute @@toStringTag
-    getter autocomplete
-    getter checked
-    getter current
-    getter invalid
-    getter keyShortcuts
-    getter label
-    getter live
-    getter orientation
-    getter placeholder
-    getter relevant
-    getter role
-    getter roleDescription
-    getter sort
-    getter valueText
-    method constructor
-    setter autocomplete
-    setter checked
-    setter current
-    setter invalid
-    setter keyShortcuts
-    setter label
-    setter live
-    setter orientation
-    setter placeholder
-    setter relevant
-    setter role
-    setter roleDescription
-    setter sort
-    setter valueText
 interface AmbientLightSensor : Sensor
     attribute @@toStringTag
     getter illuminance
@@ -1713,7 +1682,6 @@ interface DynamicsCompressorNode : AudioNode
 interface Element : Node
     attribute @@toStringTag
     attribute @@unscopables
-    getter accessibleNode
     getter assignedSlot
     getter attributes
     getter childElementCount