[api] use object instead of map for headers (#567)

This patch:

- switches to objects instead of maps for headers (in Request, Response and
page.setExtraHTTPHeaders)
- converts all header names to lower case

Fixes #547, fixes #509

lib/NetworkManager.js

@@ -29,8 +29,8 @@ class NetworkManager extends EventEmitter {
     this._requestIdToRequest = new Map();
     /** @type {!Map<string, !Request>} */
     this._interceptionIdToRequest = new Map();
-    /** @type {!Map<string, string>} */
-    this._extraHTTPHeaders = new Map();
+    /** @type {!Object<string, string>} */
+    this._extraHTTPHeaders = {};
 
     this._requestInterceptionEnabled = false;
     /** @type {!Multimap<string, string>} */
@@ -46,22 +46,21 @@ class NetworkManager extends EventEmitter {
   }
 
   /**
-   * @param {!Map<string, string>} extraHTTPHeaders
+   * @param {!Object<string, string>} extraHTTPHeaders
    * @return {!Promise}
    */
   async setExtraHTTPHeaders(extraHTTPHeaders) {
-    this._extraHTTPHeaders = new Map(extraHTTPHeaders);
-    const headers = {};
-    for (const entry of extraHTTPHeaders.entries())
-      headers[entry[0]] = entry[1];
-    await this._client.send('Network.setExtraHTTPHeaders', { headers });
+    this._extraHTTPHeaders = {};
+    for (const key of Object.keys(extraHTTPHeaders))
+      this._extraHTTPHeaders[key.toLowerCase()] = extraHTTPHeaders[key];
+    await this._client.send('Network.setExtraHTTPHeaders', { headers: this._extraHTTPHeaders });
   }
 
   /**
-   * @return {!Map<string, string>}
+   * @return {!Object<string, string>}
    */
   extraHTTPHeaders() {
-    return new Map(this._extraHTTPHeaders);
+    return Object.assign({}, this._extraHTTPHeaders);
   }
 
   /**
@@ -226,7 +225,9 @@ class Request {
     this.url = url;
     this.method = payload.method;
     this.postData = payload.postData;
-    this.headers = new Map(Object.entries(payload.headers));
+    this.headers = {};
+    for (const key of Object.keys(payload.headers))
+      this.headers[key.toLowerCase()] = payload.headers[key];
   }
 
   /**
@@ -246,18 +247,12 @@ class Request {
     console.assert(this._interceptionId, 'Request Interception is not enabled!');
     console.assert(!this._interceptionHandled, 'Request is already handled!');
     this._interceptionHandled = true;
-    let headers = undefined;
-    if (overrides.headers) {
-      headers = {};
-      for (const entry of overrides.headers)
-        headers[entry[0]] = entry[1];
-    }
     this._client.send('Network.continueInterceptedRequest', {
       interceptionId: this._interceptionId,
       url: overrides.url,
       method: overrides.method,
       postData: overrides.postData,
-      headers: headers
+      headers: overrides.headers,
     });
   }
 
@@ -288,10 +283,12 @@ class Response {
     this._request = request;
     this._contentPromise = null;
 
-    this.headers = new Map(Object.entries(headers));
     this.status = status;
     this.ok = status >= 200 && status <= 299;
     this.url = request.url;
+    this.headers = {};
+    for (const key of Object.keys(headers))
+      this.headers[key.toLowerCase()] = headers[key];
   }
 
   /**