Reflect HeadersInit changes

[annevk]

This is a change for whatwg/fetch#418 and also
aligns with the recent IDL change to replace OpenEndedDictionary with
record.

[wpt-pr-bot]

Notifying @jdm and @youennf. (Learn how reviewing works.)

[wpt-stability-bot]

Firefox

Testing revision 350ba2a386e89f6027f00d56cbc847b89e964d23
Starting 10 test iterations
All results were stable

All results

/fetch/api/headers/headers-basic.html

Subtest	Results
	OK
Create headers with existing headers with custom iterator	FAIL
Create headers with existing headers	PASS
Check get method	PASS
Create headers from no parameter	PASS
Create headers from empty object	PASS
Create headers with record	PASS
Check forEach method	FAIL
Check has method	PASS
Check values method	FAIL
Check append method	PASS
Create headers with 1 should throw	PASS
Check set method	PASS
Check Symbol.iterator method	FAIL
Check entries method	FAIL
Create headers from undefined parameter	PASS
Check delete method	PASS
Create headers with null should throw	PASS
Check keys method	FAIL
Create headers with sequence	PASS

/fetch/api/headers/headers-idl.html

Subtest	Results
	OK
Headers interface: operation set(ByteString,ByteString)	PASS
Headers interface: operation append(ByteString,ByteString)	PASS
Headers interface: calling delete(ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: operation delete(ByteString)	PASS
Headers interface: operation get(ByteString)	PASS
Headers interface object name	PASS
Headers interface object length	PASS
Headers interface: calling append(ByteString,ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: existence and properties of interface prototype object's "constructor" property	PASS
Headers interface: calling get(ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: existence and properties of interface prototype object	PASS
Headers interface: calling set(ByteString,ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: new Headers() must inherit property "get" with the proper type (2)	PASS
Headers interface: existence and properties of interface object	PASS
Headers interface: new Headers() must inherit property "set" with the proper type (4)	PASS
Headers interface: calling has(ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: new Headers() must inherit property "append" with the proper type (0)	PASS
Headers interface: new Headers() must inherit property "has" with the proper type (3)	PASS
Headers must be primary interface of new Headers()	PASS
Stringification of new Headers()	PASS
Headers interface: operation has(ByteString)	PASS
Headers interface: new Headers() must inherit property "delete" with the proper type (1)	PASS

[wpt-stability-bot]

Chrome

Testing revision 350ba2a386e89f6027f00d56cbc847b89e964d23
Starting 10 test iterations
All results were stable

All results

/fetch/api/headers/headers-basic.html

Subtest	Results
	OK
Create headers with existing headers with custom iterator	FAIL
Create headers with existing headers	PASS
Check get method	PASS
Create headers from no parameter	PASS
Create headers from empty object	PASS
Create headers with record	PASS
Check forEach method	FAIL
Check has method	PASS
Check values method	FAIL
Check append method	PASS
Create headers with 1 should throw	PASS
Check set method	PASS
Check Symbol.iterator method	FAIL
Check entries method	FAIL
Create headers from undefined parameter	FAIL
Check delete method	PASS
Create headers with null should throw	PASS
Check keys method	FAIL
Create headers with sequence	PASS

/fetch/api/headers/headers-idl.html

Subtest	Results
	OK
Headers interface: operation set(ByteString,ByteString)	PASS
Headers interface: operation append(ByteString,ByteString)	PASS
Headers interface: calling delete(ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: operation delete(ByteString)	PASS
Headers interface: operation get(ByteString)	PASS
Headers interface object name	PASS
Headers interface object length	PASS
Headers interface: calling append(ByteString,ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: existence and properties of interface prototype object's "constructor" property	PASS
Headers interface: calling get(ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: existence and properties of interface prototype object	FAIL
Headers interface: calling set(ByteString,ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: new Headers() must inherit property "get" with the proper type (2)	PASS
Headers interface: existence and properties of interface object	PASS
Headers interface: new Headers() must inherit property "set" with the proper type (4)	PASS
Headers interface: calling has(ByteString) on new Headers() with too few arguments must throw TypeError	PASS
Headers interface: new Headers() must inherit property "append" with the proper type (0)	PASS
Headers interface: new Headers() must inherit property "has" with the proper type (3)	PASS
Headers must be primary interface of new Headers()	PASS
Stringification of new Headers()	PASS
Headers interface: operation has(ByteString)	PASS
Headers interface: new Headers() must inherit property "delete" with the proper type (1)	PASS