gyp: use a set() in DeepDependencies for less O(n^2).

pylib/gyp/input.py

Index: pylib/gyp/input.py
diff --git a/pylib/gyp/input.py b/pylib/gyp/input.py
index f694e57b9fe455197bcd5eb423c48b66a8f0376e..7bf9b4035e36cc97d1bcb4e52286cd31bca97fa7 100644
--- a/pylib/gyp/input.py
+++ b/pylib/gyp/input.py
@@ -1602,15 +1602,22 @@ class DependencyGraphNode(object):
   def DeepDependencies(self, dependencies=None):
     """Returns a list of all of a target's dependencies, recursively."""
     if dependencies == None:
-      dependencies = []
+      # Using a list to get ordered output and a set to do fast "is it
+      # already added" checks.
+      dependencies = ([], set())
+
+    dependency_list, dependency_set = dependencies
 
     for dependency in self.dependencies:
       # Check for None, corresponding to the root node.
-      if dependency.ref != None and dependency.ref not in dependencies:
-        dependencies.append(dependency.ref)
+      if dependency.ref is None:
+        continue
+      if dependency.ref not in dependency_set:
+        dependency_list.append(dependency.ref)
+        dependency_set.add(dependency.ref)
         dependency.DeepDependencies(dependencies)
 
-    return dependencies
+    return dependency_list
 
   def _LinkDependenciesInternal(self, targets, include_shared_libraries,
                                 dependencies=None, initial=True):