build: python3 support

Porting of files to work with both Python 2 and Python 3.

We may want to introduce a CI run that runs with Python 3 to catch
any diversions early, run PyLint to lint compatibilty or introduce
tox to run scripts against multiple versions on the CI.

This doesn't port all files, just ones required to build and submit
CLs.

We may also want to include `six` rather than our `compat` module.

Change-Id: I72bf02daade0127e2141ee750c806d4f6e277d33

tools/gn_utils.py

diff --git a/tools/gn_utils.py b/tools/gn_utils.py
index 1bc7afc..646405d 100644
--- a/tools/gn_utils.py
+++ b/tools/gn_utils.py
@@ -24,6 +24,7 @@
 import shutil
 import subprocess
 import sys
+from compat import iteritems
 
 
 BUILDFLAGS_TARGET = '//gn:gen_buildflags'
@@ -98,7 +99,7 @@
     source files in the amalgamated result.
     """
     targets = [t.replace('//', '') for t in targets]
-    with open(os.devnull, 'rw') as devnull:
+    with open(os.devnull, 'w') as devnull:
         stdout = devnull if quiet else None
         subprocess.check_call([_tool_path('ninja')] + targets, cwd=out,
                               stdout=stdout)
@@ -246,9 +247,17 @@
             # placeholder target once we hit //gn:protoc or similar.
             self.is_third_party_dep_ = False
 
+        def __lt__(self, other):
+            if isinstance(other, self.__class__):
+                return self.name < other.name
+            raise TypeError(
+                '\'<\' not supported between instances of \'%s\' and \'%s\'' % (
+                    type(self).__name__, type(other).__name__))
+
         def __repr__(self):
-            return json.dumps({k:(list(v) if isinstance(v, set) else v)
-                    for (k,v) in self.__dict__.iteritems()}, indent=4)
+            return json.dumps({k:(list(sorted(v)) if isinstance(v, set) else v)
+                    for (k,v) in iteritems(self.__dict__)}, indent=4,
+                    sort_keys=True)
 
         def update(self, other):
             for key in ('cflags', 'defines', 'deps', 'include_dirs', 'ldflags',