Add FilePath to base namespace.

This updates headers that forward-declare it and a few random places to use the namespace explicitly. There us a using declaration in file_path.h that makes the rest compile, which we can do in future passes.
Review URL: https://codereview.chromium.org/12163003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@180245 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/sql/connection.cc b/sql/connection.cc
index aefac60f..5c0c15d 100644
--- a/sql/connection.cc
+++ b/sql/connection.cc
@@ -128,7 +128,7 @@
   Close();
 }
 
-bool Connection::Open(const FilePath& path) {
+bool Connection::Open(const base::FilePath& path) {
 #if defined(OS_WIN)
   return OpenInternal(WideToUTF8(path.value()));
 #elif defined(OS_POSIX)