Allow SessionService to be disabled.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 98d603e22c36ffb5da5c1bd39b1a0d2f209f7dcf..cdfb0b8c5493e03af2150b6f6abd0b57693256cc 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -230,6 +230,10 @@
       # plugins to make call of the main thread.
       'enable_pepper_threading%': 0,
 
+      # Enables use of the session service, which is enabled by default.
+      # Support for disabling depends on the platform.
+      'enable_session_service%': 1,
+
       # Enables theme support, which is enabled by default.  Support for
       # disabling depends on the platform.
       'enable_themes%': 1,
@@ -497,6 +501,7 @@
     'enable_web_intents_tag%': '<(enable_web_intents_tag)',
     'enable_plugin_installation%': '<(enable_plugin_installation)',
     'enable_protector_service%': '<(enable_protector_service)',
+    'enable_session_service%': '<(enable_session_service)',
     'enable_themes%': '<(enable_themes)',
     'linux_use_gold_binary%': '<(linux_use_gold_binary)',
     'linux_use_gold_flags%': '<(linux_use_gold_flags)',
@@ -788,6 +793,9 @@
         # Android does not support themes.
         'enable_themes%': 0,
 
+        # Sessions are store separately in the Java side.
+        'enable_session_service%': 0,
+
         # Set to 1 once we have a notification system for Android.
         # http://crbug.com/115320
         'notifications%': 0,
@@ -1368,6 +1376,9 @@
       ['enable_protector_service==1', {
         'defines': ['ENABLE_PROTECTOR_SERVICE=1'],
       }],
+      ['enable_session_service==1', {
+        'defines': ['ENABLE_SESSION_SERVICE=1'],
+      }],
       ['enable_themes==1', {
         'defines': ['ENABLE_THEMES=1'],
       }],