• Treat any non-Request arg to new Request() as string url
• Support Tolerance Provision when parsing HTTP headers

Android 4.0 compatibility:

• Fix reading ArrayBuffer into string on older browsers
• Only define arrayBuffer() if Blob is also supported

Android 4.0 compatibility:

• Fix reading ArrayBuffer into string on older browsers
• Only define arrayBuffer() if Blob is also supported

This changes the behavior of Headers regarding handling of headers with multiple values. Most notably, it removes the Headers.getAll() method. This diverges from the native implementations of Chrome and Firefox, since those vendors implement an earlier, now outdated version of the spec. The polyfill now acts more similar to Microsoft Edge implementation.

Consider this Headers object:

var h = new Headers()
h.append('accept', 'text/html')
h.append('accept', 'text/plain')
h.append('content-type', 'application/json')

Before:

• h.get('accept') returned text/html
• h.getAll('accept') returned an array of values
• h.forEach (and other iterables) did distinct iterations for each
  value of the same header

Now:

• h.get('accept') returns text/html,text/plain
• h.getAll() is no more
• h.forEach() (and other iterables) now only do one iteration for each unique header name, regardless of whether it had multiple values

This is in accordance with Section 3.1.2 of the spec, "combine" concept.

Spec compatibility:

• 1st argument to Request constructor must be string or Request
• Always construct a new Request instance in fetch()
• Always construct a new Headers instance in Response
• Avoid consuming body when cloning
• Add support for TypedArray/DataView as POST body
• ArrayBuffer, TypedArray, and Dataview bodies can now be accessed through any of the arrayBuffer(), text(), or blob() methods
• Default Response status is 200 OK

Other fixes:

• Make X-Request-URL header case-insensitive
• Allow reusing the same GET Request instance multiple times
• Rework parsing of raw response HTTP headers
• Attach FileReader event handlers before calling its read* method

• Reject promise on request timeout
• Guard against xhr.getAllResponseHeaders() being null

• Reject promise on request timeout
• Add support for URLSearchParams request body
• Add Headers iterable methods: keys, values, and entries
• No longer compatible with IE9: IE10+ required

• Make fetch add a Content-Type header based on the type of the body
• Handle cases where self isn't defined

• Allow making a POST request with an ArrayBuffer body