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/chromeos/chromeos_test_utils.cc b/chromeos/chromeos_test_utils.cc
index 3455644..90ee92a9 100644
--- a/chromeos/chromeos_test_utils.cc
+++ b/chromeos/chromeos_test_utils.cc
@@ -13,8 +13,8 @@
 
 bool GetTestDataPath(const std::string& component,
                      const std::string& filename,
-                     FilePath* data_dir) {
-  FilePath path;
+                     base::FilePath* data_dir) {
+  base::FilePath path;
   if (!PathService::Get(base::DIR_SOURCE_ROOT, &path))
     return false;
   path = path.Append(FILE_PATH_LITERAL("chromeos"));