Consider Zoom factor when getting bounding rect.

third_party/WebKit/Source/web/mac/WebSubstringUtil.mm

 /*
  * Copyright (C) 2005, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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
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@@ skipping 95 matching lines @@
         [string setAttributes:attrs range:NSMakeRange(position, numCharacters)];
         position += numCharacters;
     }
     return [string autorelease];
 }
 
 WebPoint getBaselinePoint(FrameView* frameView, const EphemeralRange& range, NSAttributedString* string)
 {
     // Compute bottom left corner and convert to AppKit coordinates.
     // TODO(yosin) We shold avoid to create |Range| object. See crbug.com/529985.
-    IntRect stringRect = enclosingIntRect(createRange(range)->boundingRect());
+    IntRect stringRect = frameView->contentsToRootFrame(createRange(range)->boundingBox());

[keishi, 2016/01/29 05:49:14]

According to the comment boundingRect considers css transforms. Did you need to
change it to boundingBox?

[Shu Chen, 2016/01/29 05:57:59]

If using boundingRect, the result is wrong for zoom'ed page.

How can I verify wether boundingBox can work well with css transforms?

[yosin_UTC9, 2016/01/29 06:30:52]

Add CSS property "-webkit-transform", e.g. -webkit-transform: rotate(45deg)
https://developer.mozilla.org/en-US/docs/Web/CSS/transform

     IntPoint stringPoint = stringRect.minXMaxYCorner();
     stringPoint.setY(frameView->height() - stringPoint.y());
 
     // Adjust for the font's descender. AppKit wants the baseline point.
     if ([string length]) {
         NSDictionary* attributes = [string attributesAtIndex:0 effectiveRange:NULL];
         if (NSFont* font = [attributes objectForKey:NSFontAttributeName])
             stringPoint.move(0, ceil(-[font descender]));
     }
     return stringPoint;
@@ skipping 40 matching lines @@
     if (ephemeralRange.isNull())
         return nil;
 
     NSAttributedString* result = attributedSubstringFromRange(ephemeralRange);
     if (baselinePoint)
         *baselinePoint = getBaselinePoint(frame->view(), ephemeralRange, result);
     return result;
 }
 
 } // namespace blink