MDL-60733 core: B/C for google_oauth

The google_oauth class extends oauth2client which was modified to send "Accept" headers.

The "Accept" headers break picasa and could break any other plugin that was using google_oauth.

lib/googleapi.php

@@ -448,4 +448,17 @@ class google_oauth extends oauth2_client {
         $this->header = array();
         $this->response = array();
     }
+
+    /**
+     * Make a HTTP request, we override the parents because we do not
+     * want to send accept headers (this was a change in the parent class and we want to keep the old behaviour).
+     *
+     * @param string $url The URL to request
+     * @param array $options
+     * @param mixed $acceptheader Not used.
+     * @return bool
+     */
+    protected function request($url, $options = array(), $acceptheader = 'application/json') {
+        return parent::request($url, $options, false);
+    }
 }

lib/oauthlib.php

@@ -546,9 +546,10 @@ abstract class oauth2_client extends curl {
      *
      * @param string $url The URL to request
      * @param array $options
+     * @param mixed $acceptheader mimetype (as string) or false to skip sending an accept header.
      * @return bool
      */
-    protected function request($url, $options = array()) {
+    protected function request($url, $options = array(), $acceptheader = 'application/json') {
         $murl = new moodle_url($url);
 
         if ($this->accesstoken) {
@@ -561,7 +562,9 @@ abstract class oauth2_client extends curl {
         }
 
         // Force JSON format content in response.
-        $this->setHeader('Accept: application/json');
+        if ($acceptheader) {
+            $this->setHeader('Accept: ' . $acceptheader);
+        }
 
         return parent::request($murl->out(false), $options);
     }