Refactor some more BrowserMain code. Move core code that's required by all embedders to content.

content/content_browser.gypi

Index: content/content_browser.gypi
===================================================================
--- content/content_browser.gypi	(revision 100153)
+++ content/content_browser.gypi	(working copy)
@@ -570,6 +570,13 @@
             '../build/linux/system.gyp:x11',
             '../dbus/dbus.gyp:dbus',
           ],
+          'conditions': [
+            ['linux_sandbox_path != ""', {
+              'defines': [
+                'LINUX_SANDBOX_PATH="<(linux_sandbox_path)"',
+              ],
+            }],
+          ],
         }],
         ['OS=="linux" and toolkit_views==1',{
           'dependencies': [