Compile with enable_mdns by default on Windows and Linux

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 92e67d59dcf2f06d662ba39839b93a7c861e471b..7f217a56f284ef96168723df8ded8dcbef44d37d 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -423,6 +423,7 @@
       'spdy_proxy_auth_origin%' : '',
       'spdy_proxy_auth_property%' : '',
       'spdy_proxy_auth_value%' : '',
+      'enable_mdns%' : 0,
 
       'conditions': [
         # A flag for POSIX platforms
@@ -686,6 +687,9 @@
         }, {
           'use_openmax_dl_fft%': 0,
         }],
+        ['OS=="win" or OS=="linux"', {
+            'enable_mdns%' : 1,
+        }]
       ],
 
       # Set this to 1 to enable use of concatenated impulse responses
@@ -837,6 +841,7 @@
     'spdy_proxy_auth_origin%': '<(spdy_proxy_auth_origin)',
     'spdy_proxy_auth_property%': '<(spdy_proxy_auth_property)',
     'spdy_proxy_auth_value%': '<(spdy_proxy_auth_value)',
+    'enable_mdns%' : '<(enable_mdns)',
 
     # Use system mesa instead of bundled one.
     'use_system_mesa%': 0,
@@ -1097,9 +1102,6 @@
     # rlz codes for searches but do not use the library.
     'enable_rlz%': 0,
 
-    # MDNS is disabled by default.
-    'enable_mdns%' : 0,
-
     'conditions': [
       # The version of GCC in use, set later in platforms that use GCC and have
       # not explicitly chosen to build with clang. Currently, this means all