Make favicons for about:history and about:bookmarks switch from lodpi to hidpi when dragging browser

chrome/browser/resources/shared/js/util.js

Index: chrome/browser/resources/shared/js/util.js
diff --git a/chrome/browser/resources/shared/js/util.js b/chrome/browser/resources/shared/js/util.js
index 29cdd96b442971e52461f4b4c869138e24396ba5..bfe1e1482b1ff3093f7d29dc9dfc90b3c554b037 100644
--- a/chrome/browser/resources/shared/js/util.js
+++ b/chrome/browser/resources/shared/js/util.js
@@ -38,6 +38,22 @@ function chromeSend(name, params, callbackName, callback) {
 }
 
 /**
+ * Returns the scale factors supported by this platform.
+ * @return {array} The supported scale factors.
+ */
+function getSupportedScaleFactors() {
+  var supported_scale_factors = new Array();

[kevers, 2013/01/04 20:21:10]

Using C++ naming convention here and below.  Should use camel-case naming in
Javascript.  Underscores appear in optional parameters that start with the
"opt_" prefix and at the end of private data members.

Also prefer "[]" to "new Array()", but this just a style preference.

[pkotwicz, 2013/01/04 21:21:39]

Done.

[Dan Beam, 2013/01/04 21:34:28]

This is not just style, [] always invokes the builtin Array constructor whereas
if somebody redefines window.Array new Array() invokes that code.  This was used
in a famous Gmail contacts hack. 
http://jeremiahgrossman.blogspot.com/2006/01/advanced-web-attack-techniques-u...

+  if (cr.isMac || cr.isChromeOS) {
+    supported_scale_factors.push(1);
+    supported_scale_factors.push(2);
+  } else {
+    // Windows must be restarted to display at a different scale factor.
+    supported_scale_factors.push(window.devicePixelRatio);
+  }
+  return supported_scale_factors;
+}
+
+/**
  * Generates a CSS url string.
  * @param {string} s The URL to generate the CSS url for.
  * @return {string} The CSS url string.
@@ -57,6 +73,37 @@ function url(s) {
 }
 
 /**
+ * Generates a CSS -webkit-image-set for a chrome:// url.
+ * An entry in the image set is added for each of getSupportedScaleFactors().
+ * The scale-factor-specific url is generated by replacing the first instance of
+ * 'scalefactor' in |path| with the numeric scale factor.
+ * @param {string} path The URL to generate an image set for.
+ *     'scalefactor' should be a substring of |path|.
+ * @return {string} The CSS -webkit-image-set.
+ */
+function imageset(path) {
+  var supported_scale_factors = getSupportedScaleFactors();
+
+  var replace_start_index = path.indexOf('scalefactor');
+  if (replace_start_index < 0)
+    return;
+
+  var s = '';
+  for (var i = 0; i < supported_scale_factors.length; ++i) {
+    var scale_factor = supported_scale_factors[i];
+    var path_with_scale_factor =
+        path.substr(0, replace_start_index) + scale_factor +
+        path.substr(replace_start_index + 11);
+
+   s += url(path_with_scale_factor) + ' ' + scale_factor + 'x';
+
+   if (i != supported_scale_factors.length - 1)
+     s += ', ';
+  }
+  return '-webkit-image-set(' + s + ')';
+}
+
+/**
  * Parses query parameters from Location.
  * @param {string} location The URL to generate the CSS url for.
  * @return {object} Dictionary containing name value pairs for URL
@@ -228,15 +275,32 @@ function appendParam(url, key, value) {
 }
 
 /**
- * Creates a new URL for a favicon request.
+ * Creates a CSS -webkit-image-set for a favicon request.
+ * @param {string} url The url for the favicon.
+ * @param {number=} opt_size Optional preferred size of the favicon.
+ * @param {boolean=} opt_sessionFavicon Optional flag to indicate if
+ *     requesting a session favicon.
+ * @return {string} -webkit-image-set for the favicon.
+ */
+function getFaviconImageSet(url, opt_size, opt_sessionFavicon) {
+  var size = opt_size || 16;
+  var type = opt_sessionFavicon ? 'session-favicon' : 'favicon';
+  return imageset(
+      'chrome://' + type + '/size/' + size + '@scalefactorx/' + url);
+}
+
+/**
+ * Creates a new URL for a request of the 1x favicon.
  * @param {string} url The url for the favicon.
  * @param {number=} opt_size Optional preferred size of the favicon.
+ * @param {boolean=} opt_sessionFavicon Optional flag to indicate if
+ *     requesting a session favicon.
  * @return {string} Updated URL for the favicon.
  */
-function getFaviconUrl(url, opt_size) {
+function get1xFaviconUrl(url, opt_size, opt_sessionFavicon) {
   var size = opt_size || 16;
-  return 'chrome://favicon/size/' + size + '@' +
-      window.devicePixelRatio + 'x/' + url;
+  var type = opt_sessionFavicon ? 'session-favicon' : 'favicon';
+  return 'chrome://' + type + '/size/' + size + '@1x/' + url;
 }
 
 /**