Auto merge of #12467 - jeenalee:jeena-headersAPI, r=jdm

Add the append method for the Headers API

<!-- Please describe your changes on the following line: -->
This commit adds the append method for the Headers API. @malisas and I are both contributors.

There are a few TODOs related:
- The script needs to parse the header value for certain header names to decide the header group it belongs
- There are possible spec bugs that could change what a valid header value looks like (related: [issue page](https://github.com/whatwg/fetch/issues/332))

There are WPT tests already written for the Headers API, but they will fail as the Headers API is not fully implemented.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because tests for the Headers API already exists, but this commit does not implement the interface fully. The tests will fail.

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

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tests/unit/script/headers.rs

@@ -0,0 +1,74 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use script::dom::bindings::str::ByteString;
+use script::dom::headers;
+
+#[test]
+fn test_normalize_empty_bytestring() {
+    // empty ByteString test
+    let empty_bytestring = ByteString::new(vec![]);
+    let actual = headers::normalize_value(empty_bytestring);
+    let expected = ByteString::new(vec![]);
+    assert_eq!(actual, expected);
+}
+
+#[test]
+fn test_normalize_all_whitespace_bytestring() {
+    // All whitespace test. A horizontal tab, a line feed, a carriage return , and a space
+    let all_whitespace_bytestring = ByteString::new(vec![b'\t', b'\n', b'\r', b' ']);
+    let actual = headers::normalize_value(all_whitespace_bytestring);
+    let expected = ByteString::new(vec![]);
+    assert_eq!(actual, expected);
+}
+
+#[test]
+fn test_normalize_non_empty_no_whitespace_bytestring() {
+    // Non-empty, no whitespace ByteString test
+    let no_whitespace_bytestring = ByteString::new(vec![b'S', b'!']);
+    let actual = headers::normalize_value(no_whitespace_bytestring);
+    let expected = ByteString::new(vec![b'S', b'!']);
+    assert_eq!(actual, expected);
+}
+
+#[test]
+fn test_normalize_non_empty_leading_whitespace_bytestring() {
+    // Non-empty, leading whitespace, no trailing whitespace ByteString test
+    let leading_whitespace_bytestring = ByteString::new(vec![b'\t', b'\n', b' ', b'\r', b'S', b'!']);
+    let actual = headers::normalize_value(leading_whitespace_bytestring);
+    let expected = ByteString::new(vec![b'S', b'!']);
+    assert_eq!(actual, expected);
+}
+
+#[test]
+fn test_normalize_non_empty_no_leading_whitespace_trailing_whitespace_bytestring() {
+    // Non-empty, no leading whitespace, but with trailing whitespace ByteString test
+    let trailing_whitespace_bytestring = ByteString::new(vec![b'S', b'!', b'\t', b'\n', b' ', b'\r']);
+    let actual = headers::normalize_value(trailing_whitespace_bytestring);
+    let expected = ByteString::new(vec![b'S', b'!']);
+    assert_eq!(actual, expected);
+}
+
+#[test]
+fn test_normalize_non_empty_leading_and_trailing_whitespace_bytestring() {
+    // Non-empty, leading whitespace, and trailing whitespace ByteString test
+    let whitespace_sandwich_bytestring =
+        ByteString::new(vec![b'\t', b'\n', b' ', b'\r', b'S', b'!', b'\t', b'\n', b' ', b'\r']);
+    let actual = headers::normalize_value(whitespace_sandwich_bytestring);
+    let expected = ByteString::new(vec![b'S', b'!']);
+    assert_eq!(actual, expected);
+}
+
+#[test]
+fn test_normalize_non_empty_leading_trailing_and_internal_whitespace_bytestring() {
+    // Non-empty, leading whitespace, trailing whitespace,
+    // and internal whitespace ByteString test
+    let whitespace_bigmac_bytestring =
+        ByteString::new(vec![b'\t', b'\n', b' ', b'\r', b'S',
+                             b'\t', b'\n', b' ', b'\r', b'!',
+                             b'\t', b'\n', b' ', b'\r']);
+    let actual = headers::normalize_value(whitespace_bigmac_bytestring);
+    let expected = ByteString::new(vec![b'S', b'\t', b'\n', b' ', b'\r', b'!']);
+    assert_eq!(actual, expected);
+}

tests/unit/script/lib.rs

@@ -12,3 +12,4 @@ extern crate url;
 #[cfg(test)] mod origin;
 #[cfg(all(test, target_pointer_width = "64"))] mod size_of;
 #[cfg(test)] mod textinput;
+#[cfg(test)] mod headers;

tests/wpt/mozilla/tests/mozilla/interfaces.html

@@ -48,6 +48,7 @@ test_interfaces([
   "FocusEvent",
   "FormData",
   "HashChangeEvent",
+  "Headers",
   "HTMLAnchorElement",
   "HTMLAppletElement",
   "HTMLAreaElement",

tests/wpt/mozilla/tests/mozilla/interfaces.worker.js

@@ -44,6 +44,7 @@ test_interfaces([
   "FocusEvent",
   "FormData",
   "HashChangeEvent",
+  "Headers",  
   "HTMLAnchorElement",
   "HTMLAppletElement",
   "HTMLAreaElement",