tools/gn: Add out-of-line copy ctors for complex classes.

tools/gn/pattern.h

Index: tools/gn/pattern.h
diff --git a/tools/gn/pattern.h b/tools/gn/pattern.h
index 1aa709700da0e89b546f7deac2f5c70195b4df9e..f141f3eaeb18b80d81a4660081228e84d5330ee6 100644
--- a/tools/gn/pattern.h
+++ b/tools/gn/pattern.h
@@ -47,6 +47,7 @@ class Pattern {
   };
 
   explicit Pattern(const std::string& s);
+  Pattern(const Pattern& other);
   ~Pattern();
 
   // Returns true if the current pattern matches the given string.
@@ -70,6 +71,7 @@ class Pattern {
 class PatternList {
  public:
   PatternList();
+  PatternList(const PatternList& other);
   ~PatternList();
 
   bool is_empty() const { return patterns_.empty(); }