Use custom scrollbars for print preview on non-retina mac displays.

chrome/browser/resources/pdf/pdf.js

Index: chrome/browser/resources/pdf/pdf.js
diff --git a/chrome/browser/resources/pdf/pdf.js b/chrome/browser/resources/pdf/pdf.js
index c652ca4f3ad0065447aa2a45c19b8c7517bbb633..5a513e11b80f262b28fd5daf895bde765ccd40f0 100644
--- a/chrome/browser/resources/pdf/pdf.js
+++ b/chrome/browser/resources/pdf/pdf.js
@@ -75,6 +75,16 @@ function PDFViewer(streamDetails) {
       this.streamDetails_.originalUrl.indexOf('chrome://print') == 0;
   this.isMaterial_ = location.pathname.substring(1) === 'index-material.html';
 
+  // Hack to enable custom scrollbars for print preview on non-retina mac
+  // displays. Remove after crbug.com/466039 is fixed.
+  if (this.isPrintPreview_) {
+    var link = document.createElement('link');
+    link.rel = 'stylesheet';
+    link.type = 'text/css';
+    link.href = 'scrollbars-mac.css';
+    document.getElementsByTagName('head')[0].appendChild(link);
+  }
+
   // The sizer element is placed behind the plugin element to cause scrollbars
   // to be displayed in the window. It is sized according to the document size
   // of the pdf and zoom level.