Create tools/js-dep-visualizer.py.

This tools lets us view circular dependencies in our JS
code.  It does regex parsing, so it has a few false positives,
but it's an early draft of the tools.  Steve Howell helped
with this commit.

tools/js-dep-visualizer.py

@@ -0,0 +1,74 @@
+"""
+$ python ./tools/js-dep-visualizer.py
+$ dot -Tpng var/zulip-deps.dot -o var/zulip-deps.png
+"""
+
+import os
+import re
+import sys
+
+from typing import Any, Dict, List
+
+TOOLS_DIR = os.path.abspath(os.path.dirname(__file__))
+ROOT_DIR = os.path.dirname(TOOLS_DIR)
+sys.path.insert(0, ROOT_DIR)
+from tools.lib.graph import Graph, make_dot_file
+
+JS_FILES_DIR = os.path.abspath(os.path.join(ROOT_DIR, 'static/js'))
+OUTPUT_FILE_PATH = os.path.abspath(os.path.join(ROOT_DIR, 'var/zulip-deps.dot'))
+
+modules = [] # type: List[Dict[str, Any]]
+for js_file in os.listdir(JS_FILES_DIR):
+    name = js_file[:-3] # remove .js
+    file_path = os.path.abspath(os.path.join(JS_FILES_DIR, js_file))
+
+    if os.path.isfile(file_path) and js_file != '.eslintrc.json':
+        modules.append(dict(
+            filename=js_file,
+            name=name,
+            path=file_path,
+            regex=re.compile('[^_]{}\.\w+\('.format(name))
+        ))
+
+tuples = set()
+for module in modules:
+
+    other_modules = filter(lambda x: x['name'] != module['name'], modules)
+
+    with open(module['path']) as f:
+        module_content = f.read()
+        for other_module in other_modules:
+            dependencies = re.findall(other_module['regex'], module_content)
+            if dependencies:
+                parent = module['name']
+                child = other_module['name']
+                tup = (parent, child)
+                if tup == ('stream_data', 'subs'):
+                    continue # parsing mistake due to variable called "subs"
+                tuples.add(tup)
+
+# print(tuples)
+graph = Graph(*tuples)
+tricky_modules = [
+    'blueslip',
+    'channel',
+    'filter',
+    'hashchange',
+    'message_store',
+    'narrow',
+    'popovers',
+    'reload',
+    'resize',
+    'server_events', # has restart code
+    'socket',
+    'stream_color',
+    'ui',
+    'zulip', # zulip.com false positives
+]
+for node in tricky_modules:
+    graph.remove(node)
+graph.remove_exterior_nodes()
+buffer = make_dot_file(graph)
+
+with open(OUTPUT_FILE_PATH, 'w') as f:
+    f.write(buffer)