Add syncable_prefs namespace.

Move all the code in the syncable_prefs components into the namespace
syncable_prefs and fix usage.

Change automated with tools/git/mffr.py with manual fixes for the
class forward-declaration.

BUG=520542
[email protected]

Review URL: https://codereview.chromium.org/1353913003

Cr-Commit-Position: refs/heads/master@{#349638}
diff --git a/chrome/browser/font_family_cache_unittest.cc b/chrome/browser/font_family_cache_unittest.cc
index c11471c..412f2bf 100644
--- a/chrome/browser/font_family_cache_unittest.cc
+++ b/chrome/browser/font_family_cache_unittest.cc
@@ -35,7 +35,8 @@
   content::TestBrowserThreadBundle thread_bundle_;
   TestingProfile profile;
   TestingFontFamilyCache cache(&profile);
-  TestingPrefServiceSyncable* prefs = profile.GetTestingPrefService();
+  syncable_prefs::TestingPrefServiceSyncable* prefs =
+      profile.GetTestingPrefService();
 
   std::string font1("font 1");
   std::string font2("font 2");