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/static_request.ts

@@ -6,7 +6,8 @@ import {
   RegExpWrapper,
   CONST_EXPR,
   isPresent,
-  isJsObject
+  isJsObject,
+  StringWrapper
 } from 'angular2/src/facade/lang';
 
 // TODO(jeffbcross): properly implement body accessors
@@ -39,7 +40,19 @@ export class Request {
   cache: RequestCacheOpts;
   constructor(requestOptions: RequestOptions) {
     // TODO: assert that url is present
+    let url = requestOptions.url;
     this.url = requestOptions.url;
+    if (isPresent(requestOptions.search)) {
+      let search = requestOptions.search.toString();
+      if (search.length > 0) {
+        let prefix = '?';
+        if (StringWrapper.contains(this.url, '?')) {
+          prefix = (this.url[this.url.length - 1] == '&') ? '' : '&';
+        }
+        // TODO: just delete search-query-looking string in url?
+        this.url = url + prefix + search;
+      }
+    }
     this._body = requestOptions.body;
     this.method = requestOptions.method;
     // TODO(jeffbcross): implement behavior