Add DOMString floating point string test and fix

Fixes an issue where DOMString::is_valid_floating_point_number_string
was returning true for strings that began with whitespace characters-
TAB, LF, FF, or CR. Also added a unit test to cover this since the
corresponding web-platform-tests are incomplete.

components/script/dom/bindings/str.rs

@@ -3,11 +3,11 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 //! The `ByteString` struct.
-
 use chrono::prelude::{Utc, Weekday};
 use chrono::{Datelike, TimeZone};
 use cssparser::CowRcStr;
 use html5ever::{LocalName, Namespace};
+use regex::Regex;
 use servo_atoms::Atom;
 use std::borrow::{Borrow, Cow, ToOwned};
 use std::default::Default;
@@ -337,11 +337,11 @@ impl DOMString {
 
     /// https://html.spec.whatwg.org/multipage/#valid-floating-point-number
     pub fn is_valid_floating_point_number_string(&self) -> bool {
-        // for the case that `parse_floating_point_number` cannot handle
-        if self.0.contains(" ") {
-            return false;
+        lazy_static! {
+            static ref RE: Regex =
+                Regex::new(r"^-?(?:\d+\.\d+|\d+|\.\d+)(?:(e|E)(\+|\-)?\d+)?$").unwrap();
         }
-        parse_floating_point_number(&self.0).is_ok()
+        RE.is_match(&self.0) && parse_floating_point_number(&self.0).is_ok()
     }
 
     /// https://html.spec.whatwg.org/multipage/#best-representation-of-the-number-as-a-floating-point-number

tests/unit/script/domstring.rs

@@ -0,0 +1,20 @@
+// Copyright 2013 The Servo Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use script::test::DOMString;
+
+#[test]
+fn test_domstring_is_valid_floating_point_number_string_leading_whitespace() {
+    assert!(!DOMString::from("\t1").is_valid_floating_point_number_string());
+    assert!(!DOMString::from("\n1").is_valid_floating_point_number_string());
+    // \x0C - form feed
+    assert!(!DOMString::from("\x0C1").is_valid_floating_point_number_string());
+    assert!(!DOMString::from("\r1").is_valid_floating_point_number_string());
+    assert!(!DOMString::from(" 1").is_valid_floating_point_number_string());
+}

tests/unit/script/lib.rs

@@ -2,6 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
+#[cfg(test)]
+mod domstring;
 #[cfg(test)]
 mod headers;
 #[cfg(test)]