Out of line CallbackBase's copy and assignment operators.

This saved nearly 300KiB on a release build of Chrome.

BUG=436357

Review URL: https://codereview.chromium.org/760513002

Cr-Commit-Position: refs/heads/master@{#305784}


CrOS-Libchrome-Original-Commit: f883604e3ea3a0b9881dc5eb1e933fb66d914003
diff --git a/base/callback_internal.h b/base/callback_internal.h
index 9dca023..8a5c437 100644
--- a/base/callback_internal.h
+++ b/base/callback_internal.h
@@ -36,6 +36,9 @@
 // template bloat.
 class BASE_EXPORT CallbackBase {
  public:
+  CallbackBase(const CallbackBase& c);
+  CallbackBase& operator=(const CallbackBase& c);
+
   // Returns true if Callback is null (doesn't refer to anything).
   bool is_null() const { return bind_state_.get() == NULL; }