Add default browser checking and setting on Linux.

DEPS

 vars = {
   "webkit_trunk":
     "http://svn.webkit.org/repository/webkit/trunk",
   "webkit_revision": "45673",
 }
 
 
 deps = {
   "src/breakpad/src":
     "http://google-breakpad.googlecode.com/svn/trunk/src@346",
@@ skipping 66 matching lines @@
       "/trunk/deps/third_party/python_24@19441",
   },
   "mac": {
     "src/third_party/GTM":
       "http://google-toolbox-for-mac.googlecode.com/svn/trunk@119",
     "src/third_party/pdfsqueeze":
       "http://pdfsqueeze.googlecode.com/svn/trunk@2",
     "src/third_party/WebKit/WebKit/mac":
       Var("webkit_trunk") + "/WebKit/mac@" + Var("webkit_revision"),
   },
+  "unix": {
+    "src/third_party/xdg-utils":
+      "/trunk/deps/third_party/xdg-utils@20073",
+  },
 }
 
 
 include_rules = [
   # Everybody can use some things.
   "+base",
   "+build",
 
   # For now, we allow ICU to be included by specifying "unicode/...", although
   # this should probably change.
@@ skipping 20 matching lines @@
 
 
 hooks = [
   {
     # A change to a .gyp, .gypi, or to GYP itself shound run the generator.
     "pattern": "\\.gypi?$|[/\\\\]src[/\\\\]tools[/\\\\]gyp[/\\\\]",
     "action": ["python", "src/tools/gyp/gyp_dogfood", "src/build/all.gyp"],
   },
 ]