Do regular expression for camelCase CSS processing in JS.

tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate

Index: tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate b/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
index ce96ec89471f1d2c5963e2543a03dc1d0a03baa1..a32d903be8c722ce9131dbc2b12d0a5134a24ffa 100644
--- a/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
+++ b/tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate
@@ -76,10 +76,18 @@ $endif
   }
 
   static String _camelCase(String hyphenated) {
+$if DART2JS
+    var replacedMs = JS('String', r'#.replace(/^-ms-/, "ms-")', hyphenated);
+
+    var fToUpper = const JS_CONST(
+        r'function(_, letter) { return letter.toUpperCase(); }');
+    return JS('String', r'#.replace(/-([\da-z])/ig, #)', replacedMs, fToUpper);
+$else
     // The "ms" prefix is always lowercased.
     return hyphenated.replaceFirst(new RegExp('^-ms-'), 'ms-').replaceAllMapped(
         new RegExp('-([a-z]+)', caseSensitive: false),
         (match) => match[0][1].toUpperCase() + match[0].substring(2));
+$endif
   }
 
 $if DART2JS