build: explain how to test Python 3.6 or 3.7

This helps contributors understand how they can test Python 3.6 or 3.7
on Travis CI.

Helps with issues like:
- nodejs#29246 (comment)

.travis.yml

@@ -10,9 +10,9 @@ language: cpp
 # To experiment with Python 3, comment out Python 2.7 and uncomment one of the Python 3 versions.
 env:
   global:
-    - PYTHON_VERSION="2.7.15"
+    # - PYTHON_VERSION="2.7.15"
     # - PYTHON_VERSION="3.6.7"
-    # - PYTHON_VERSION="3.7.1"
+    - PYTHON_VERSION="3.7.1"
 jobs:
   include:
     - stage: "Compile"

deps/v8/third_party/inspector_protocol/code_generator.py

@@ -43,6 +43,9 @@ def json_object_hook(object_dict):
       items = [(k, os.path.join(output_base, v) if k == "output" else v)
                for (k, v) in items]
       keys, values = list(zip(*items))
+      # 'async' is a Python 3.7+ keyword.  Don't use namedtuple(rename=True)
+      # because that would only rename async on Python 3 but not on Python 2.
+      keys = ['async_' if k == 'async' else k for k in keys]
       return collections.namedtuple('X', keys)(*values)
     return json.loads(data, object_hook=json_object_hook)
 
@@ -555,7 +558,7 @@ def is_async_command(self, domain, command):
     if not self.config.protocol.options:
       return False
     return self.check_options(self.config.protocol.options, domain, command,
-                              "async", None, False)
+                              "async_", None, False)
 
   def is_exported(self, domain, name):
     if not self.config.protocol.options:

tools/inspector_protocol/code_generator.py

@@ -41,6 +41,9 @@ def json_object_hook(object_dict):
             items = [(k, os.path.join(output_base, v) if k == "path" else v) for (k, v) in object_dict.items()]
             items = [(k, os.path.join(output_base, v) if k == "output" else v) for (k, v) in items]
             keys, values = list(zip(*items))
+            # 'async' is a python 3 keyword. Don't use namedtuple(rename=True)
+            # because that only renames it in python 3 but not python 2.
+            keys = tuple('async_' if k == 'async' else k for k in keys)
             return collections.namedtuple('X', keys)(*values)
         return json.loads(data, object_hook=json_object_hook)
 
@@ -521,7 +524,7 @@ def generate_type(self, domain, typename):
     def is_async_command(self, domain, command):
         if not self.config.protocol.options:
             return False
-        return self.check_options(self.config.protocol.options, domain, command, "async", None, False)
+        return self.check_options(self.config.protocol.options, domain, command, "async_", None, False)
 
 
     def is_exported(self, domain, name):