fix headers common, tests pass: closes angular#5742

src/ng/http.js

@@ -111,9 +111,9 @@ function $HttpProvider() {
       common: {
         'Accept': 'application/json, text/plain, */*'
       },
-      post:   CONTENT_TYPE_APPLICATION_JSON,
-      put:    CONTENT_TYPE_APPLICATION_JSON,
-      patch:  CONTENT_TYPE_APPLICATION_JSON
+      post:   copy(CONTENT_TYPE_APPLICATION_JSON),
+      put:    copy(CONTENT_TYPE_APPLICATION_JSON),
+      patch:  copy(CONTENT_TYPE_APPLICATION_JSON)
     },
 
     xsrfCookieName: 'XSRF-TOKEN',
@@ -324,7 +324,7 @@ function $HttpProvider() {
      * to `push` or `unshift` a new transformation function into the transformation chain. You can
      * also decide to completely override any default transformations by assigning your
      * transformation functions to these properties directly without the array wrapper.  These defaults
-     * are again available on the $http factory at run-time, which may be useful if you have run-time 
+     * are again available on the $http factory at run-time, which may be useful if you have run-time
      * services you wish to be involved in your transformations.
      *
      * Similarly, to locally override the request/response transforms, augment the

test/ng/httpSpec.js

@@ -1430,6 +1430,12 @@ describe('$http', function() {
 
       it('should expose the defaults object at runtime', function() {
         expect($http.defaults).toBeDefined();
+        expect($http.defaults.headers.post).not.toBe($http.defaults.headers.put);
+        expect($http.defaults.headers.post).not.toBe($http.defaults.headers.patch);
+        expect($http.defaults.headers.put).not.toBe($http.defaults.headers.patch);
+        expect($http.defaults.headers.put).not.toBe($http.defaults.headers.post);
+        expect($http.defaults.headers.patch).not.toBe($http.defaults.headers.put);
+        expect($http.defaults.headers.patch).not.toBe($http.defaults.headers.post);
 
         $http.defaults.headers.common.foo = 'bar';
         $httpBackend.expect('GET', '/url', undefined, function(headers) {