feat(http): serialize search parameters from request options

- Extends URLSearchParams API to include operations for combining
  different URLSearchParams objects:

  These new methods include:
  setAll(otherParams): performs `this.set(key, values[0])` for each
      key/value-list pair in `otherParams`

  appendAll(otherParams): performs `this.append(key, values)` for
      each key/value-list pair in `otherParams`

  replaceAll(otherParams): for each key/value-list pair in
      `otherParams`, replaces current set of values for `key` with
      a copy of the list of values.

- RequestOptions do not merge search params automatically (because
  there are multiple ways to do this). Instead, they replace any
  existing `search` field if `search` is provided. Explicit merging
  is required if merging is desirable.

- Some extra test coverage added.

Closes #2417
Closes #3020

modules/angular2/src/http/base_request_options.ts

@@ -1,8 +1,9 @@
-import {CONST_EXPR, CONST, isPresent} from 'angular2/src/facade/lang';
+import {CONST_EXPR, CONST, isPresent, isString} from 'angular2/src/facade/lang';
 import {Headers} from './headers';
 import {RequestModesOpts, RequestMethods, RequestCacheOpts, RequestCredentialsOpts} from './enums';
 import {IRequestOptions} from './interfaces';
 import {Injectable} from 'angular2/di';
+import {URLSearchParams} from './url_search_params';
 
 /**
  * Creates a request options object similar to the `RequestInit` description
@@ -33,7 +34,9 @@ export class RequestOptions implements IRequestOptions {
   credentials: RequestCredentialsOpts;
   cache: RequestCacheOpts;
   url: string;
-  constructor({method, headers, body, mode, credentials, cache, url}: IRequestOptions = {}) {
+  search: URLSearchParams;
+  constructor({method, headers, body, mode, credentials, cache, url, search}:
+                  IRequestOptions = {}) {
     this.method = isPresent(method) ? method : null;
     this.headers = isPresent(headers) ? headers : null;
     this.body = isPresent(body) ? body : null;
@@ -41,6 +44,9 @@ export class RequestOptions implements IRequestOptions {
     this.credentials = isPresent(credentials) ? credentials : null;
     this.cache = isPresent(cache) ? cache : null;
     this.url = isPresent(url) ? url : null;
+    this.search = isPresent(search) ? (isString(search) ? new URLSearchParams(<string>(search)) :
+                                                          <URLSearchParams>(search)) :
+                                      null;
   }
 
   /**
@@ -56,7 +62,11 @@ export class RequestOptions implements IRequestOptions {
       credentials: isPresent(options) && isPresent(options.credentials) ? options.credentials :
                                                                           this.credentials,
       cache: isPresent(options) && isPresent(options.cache) ? options.cache : this.cache,
-      url: isPresent(options) && isPresent(options.url) ? options.url : this.url
+      url: isPresent(options) && isPresent(options.url) ? options.url : this.url,
+      search: isPresent(options) && isPresent(options.search) ?
+                  (isString(options.search) ? new URLSearchParams(<string>(options.search)) :
+                                              (<URLSearchParams>(options.search)).clone()) :
+                  this.search
     });
   }
 }