Update polygerrit_plugin() build rule

Add support for .js based plugins, custom plugin_name to prevent
conflicts with server-side plugins with the same name.

Here's an example:
https://chromium-review.googlesource.com/c/infra/gerrit-plugins/landingwidget/+/1295049

So what we want to achieve is to have:

  gerrit_plugin(
    name = "landingwidget",
  [...]

and

  polygerrit_plugin(
    name = "landingwidget_ui",
    plugin_name = "landingwidget",
  [...]

and produce the following final artifacts:

  landingwidget.jar
  landingwidget.js

Change-Id: Ic9c68809cbaaf4650301d98e56d7c1c76e008251
(cherry picked from commit 3c1139ee68)

tools/bzl/js.bzl

@@ -428,7 +428,7 @@ def bundle_assets(*args, **kwargs):
     """Combine html, js, css files and optionally split into js and html bundles."""
     _bundle_rule(*args, pkg = native.package_name(), **kwargs)
 
-def polygerrit_plugin(name, app, srcs = [], assets = None, **kwargs):
+def polygerrit_plugin(name, app, srcs = [], assets = None, plugin_name = None, **kwargs):
     """Bundles plugin dependencies for deployment.
 
     This rule bundles all Polymer elements and JS dependencies into .html and .js files.
@@ -436,20 +436,40 @@ def polygerrit_plugin(name, app, srcs = [], assets = None, **kwargs):
     Output of this rule is a FileSet with "${name}_fs", with deploy artifacts in "plugins/${name}/static".
 
     Args:
-      name: String, plugin name.
+      name: String, rule name.
       app: String, the main or root source file.
       assets: Fileset, additional files to be used by plugin in runtime, exported to "plugins/${name}/static".
-      srcs: Source files required for combining.
+      plugin_name: String, plugin name. ${name} is used if not provided.
     """
+    if not plugin_name:
+        plugin_name = name
 
+    html_plugin = app.endswith(".html")
+    srcs = srcs if app in srcs else srcs + [app]
+
+    if html_plugin:
         # Combines all .js and .html files into foo_combined.js and foo_combined.html
         _bundle_rule(
             name = name + "_combined",
             app = app,
-        srcs = srcs if app in srcs else srcs + [app],
+            srcs = srcs,
             pkg = native.package_name(),
             **kwargs
         )
+        js_srcs = [name + "_combined.js"]
+    else:
+        js_srcs = srcs
+
+    closure_js_library(
+        name = name + "_closure_lib",
+        srcs = js_srcs,
+        convention = "GOOGLE",
+        no_closure_library = True,
+        deps = [
+            "//lib/polymer_externs:polymer_closure",
+            "//polygerrit-ui/app/externs:plugin",
+        ],
+    )
 
     closure_js_binary(
         name = name + "_bin",
@@ -464,37 +484,27 @@ def polygerrit_plugin(name, app, srcs = [], assets = None, **kwargs):
         ],
     )
 
-    closure_js_library(
+    if html_plugin:
-        name = name + "_closure_lib",
-        srcs = [name + "_combined.js"],
-        convention = "GOOGLE",
-        no_closure_library = True,
-        deps = [
-            "//lib/polymer_externs:polymer_closure",
-            "//polygerrit-ui/app/externs:plugin",
-        ],
-    )
-
         native.genrule(
             name = name + "_rename_html",
             srcs = [name + "_combined.html"],
-        outs = [name + ".html"],
+            outs = [plugin_name + ".html"],
-        cmd = "sed 's/<script src=\"" + name + "_combined.js\"/<script src=\"" + name + ".js\"/g' $(SRCS) > $(OUTS)",
+            cmd = "sed 's/<script src=\"" + name + "_combined.js\"/<script src=\"" + plugin_name + ".js\"/g' $(SRCS) > $(OUTS)",
             output_to_bindir = True,
         )
 
     native.genrule(
         name = name + "_rename_js",
         srcs = [name + "_bin.js"],
-        outs = [name + ".js"],
+        outs = [plugin_name + ".js"],
         cmd = "cp $< $@",
         output_to_bindir = True,
     )
 
-    static_files = [
+    if html_plugin:
-        name + ".js",
+        static_files = [plugin_name + ".js", plugin_name + ".html"]
-        name + ".html",
+    else:
-    ]
+        static_files = [plugin_name + ".js"]
 
     if assets:
         nested, direct = [], []