Add media router common classes and unittests.

chrome/chrome_browser.gypi

Index: chrome/chrome_browser.gypi
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index 6f9d984b1fc2791b331ddd8208327aca390b24a3..7bf2a5f9a5c4d9b4d6dad97ffa65a27ae1f896a5 100644
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -2396,6 +2396,16 @@
       'browser/search_engines/ui_thread_search_terms_data_android.cc',
       'browser/search_engines/ui_thread_search_terms_data_android.h',
     ],
+    'chrome_browser_media_router_sources': [
+      'browser/media/router/common.h',
+      'browser/media/router/media_route.cc',
+      'browser/media/router/media_route.h',
+      'browser/media/router/media_route_id.h',
+      'browser/media/router/media_sink.cc',
+      'browser/media/router/media_sink.h',
+      'browser/media/router/media_source.cc',
+      'browser/media/router/media_source.h',
+    ],
     'chrome_browser_service_discovery_sources': [
       'browser/local_discovery/cloud_device_list.cc',
       'browser/local_discovery/cloud_device_list.h',
@@ -3150,6 +3160,9 @@
         ['enable_task_manager==1', {
           'sources': [ '<@(chrome_browser_task_manager_sources)' ],
         }],
+        ['enable_media_router==1', {
+          'sources': [ '<@(chrome_browser_media_router_sources)' ],
+        }],
         ['enable_spellcheck==1', {
           'sources': [ '<@(chrome_browser_spellchecker_sources)' ],
           'dependencies': [