base: Add out-of-line copy ctors for complex classes.

This patch adds out of line copy constructors for classes that our
clang-plugin considers heavy. This is an effort to enable copy
constructor checks by default.

BUG=436357
R=dcheng@chromium.org, thakis@chromium.org

Review URL: https://codereview.chromium.org/1730873002

Cr-Commit-Position: refs/heads/master@{#377443}

diff --git a/base/version.h b/base/version.h
index 30cb735..25b570a 100644
--- a/base/version.h
+++ b/base/version.h

@@ -23,6 +23,8 @@
   // Version object is assign to it.
   Version();
 
+  Version(const Version& other);
+
   ~Version();
 
   // Initializes from a decimal dotted version number, like "0.1.1".