Add support for retrieving image thumbnails as part of the accessibility tree.

chrome/common/extensions/api/automation_internal.idl

Index: chrome/common/extensions/api/automation_internal.idl
diff --git a/chrome/common/extensions/api/automation_internal.idl b/chrome/common/extensions/api/automation_internal.idl
index 5c93adc5520cc4834c6dde7525ee4336dd46dc37..bbdf2c3ee601b757f53131ae42c2e1af1bb9f433 100644
--- a/chrome/common/extensions/api/automation_internal.idl
+++ b/chrome/common/extensions/api/automation_internal.idl
@@ -31,6 +31,7 @@ namespace automationInternal {
   enum ActionType {
     focus,
     doDefault,
+    getImageData,
     makeVisible,
     setAccessibilityFocus,
     setSequentialFocusNavigationStartingPoint,
@@ -67,6 +68,12 @@ namespace automationInternal {
     long? tabID;
   };
 
+  // Arguments for the getImageData function.
+  dictionary GetImageDataParams {
+    long maxWidth;
+    long maxHeight;
+  };
+
   // Returns the accessibility tree id of the web contents who's accessibility
   // was enabled using enableTab().
   callback EnableTabCallback = void(long tree_id);