Add a comment to PagePopupController.idl.

third_party/WebKit/Source/core/page/PagePopupController.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// PagePopupController provides functions used by form control popup
+// implementations, and it's not exposed to the Web. WebPagePopupImpl class
+// enables this interface by provideContextFeaturesTo().
 [
     NoInterfaceObject,
     RuntimeEnabled=PagePopup
 ] interface PagePopupController {
     void setValueAndClosePopup(long numberValue, DOMString stringValue);
     void setValue(DOMString value);
     void closePopup();
     void selectFontsFromOwnerDocument(Document targetDocument);
     DOMString localizeNumberString(DOMString numberString);
     DOMString formatMonth(long year, long zeroBaseMonth);
     DOMString formatShortMonth(long year, long zeroBaseMonth);
     DOMString formatWeek(long year, long weekNumber, DOMString localizedStartDate);
     // window.resizeTo/moveTo are not suitable because LocalDOMWindow adjusts
     // rectangle to fit in the current screen. Popups sometimes need to be
     // positioned on other screens.
     void setWindowRect(long x, long y,long width, long height);
 };