Move Pickle to base namespace.

Updates forward-declares and headers, but keeps a using statement in to avoid updating all users atomically.

TBR=jschuh for IPC stuff

Review URL: https://codereview.chromium.org/1149113006

Cr-Commit-Position: refs/heads/master@{#332352}


CrOS-Libchrome-Original-Commit: 05cfd8ddb3849b7e11bb53e199064291a52aeea9
diff --git a/base/files/file_path.h b/base/files/file_path.h
index 3a0513d..0c84af6 100644
--- a/base/files/file_path.h
+++ b/base/files/file_path.h
@@ -124,11 +124,11 @@
 #define FILE_PATH_USES_WIN_SEPARATORS
 #endif  // OS_WIN
 
+namespace base {
+
 class Pickle;
 class PickleIterator;
 
-namespace base {
-
 // An abstraction to isolate users from the differences between native
 // pathnames on different platforms.
 class BASE_EXPORT FilePath {