headless: Implement DevTools events

headless/lib/browser/domain_cc.template

Index: headless/lib/browser/domain_cc.template
diff --git a/headless/lib/browser/domain_cc.template b/headless/lib/browser/domain_cc.template
index 9a99bdec8e1169b977542169f7150677afafd78d..fb8ef76de9418475b7c4901ff9ec42e0d6b9cf48 100644
--- a/headless/lib/browser/domain_cc.template
+++ b/headless/lib/browser/domain_cc.template
@@ -12,7 +12,28 @@ namespace headless {
 
 namespace {{domain.domain | camelcase_to_hacker_style}} {
 
-Domain::Domain(internal::MessageDispatcher* dispatcher) : dispatcher_(dispatcher) {}
+Domain::Domain(internal::MessageDispatcher* dispatcher)
+    : dispatcher_(dispatcher) {
+  {% if "events" in domain %}
+    {# Register all events in this domain. #}
+    {% for event in domain.events %}
+  dispatcher_->RegisterEventHandler(
+      "{{domain.domain}}.{{event.name}}",
+      base::Bind(&Domain::Dispatch{{event.name | to_title_case}}Event,
+                 base::Unretained(this)));
+    {% endfor %}
+  {% endif %}
+}
+
+  {% if "events" in domain %}
+void Domain::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void Domain::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+  {% endif %}
 
 Domain::~Domain() {}
   {% for command in domain.commands %}
@@ -80,6 +101,25 @@ void Domain::Handle{{method_name}}Response(base::Callback<void(std::unique_ptr<{
   callback.Run(std::move(result));
 }
 {% endfor %}
+{% if "events" in domain %}
+  {% for event in domain.events %}
+
+{# Generate dispatchers which call registered observers for an event. #}
+void Domain::Dispatch{{event.name | to_title_case}}Event({# -#}
+    {% if "parameters" in event %}{# -#}
+    const base::Value& params{# -#}
+    {% endif %}) {
+    {% if "parameters" in event %}
+  ErrorReporter errors;
+  std::unique_ptr<{{event.name | to_title_case}}Params> parsed_params({{event.name | to_title_case}}Params::Parse(params, &errors));
+  DCHECK(!errors.HasErrors());
+  FOR_EACH_OBSERVER(Observer, observers_, On{{event.name | to_title_case}}(*parsed_params));
+    {% else %}
+  FOR_EACH_OBSERVER(Observer, observers_, On{{event.name | to_title_case}}());

[dgozman, 2016/04/21 17:21:36]

It could be easier for clients to roll new versions of protocol if every event
has params. This makes signature of event method stable and adding (yet unused)
parameter to event won't break existing code.


Similar idea applies to generated shorthands for protocol methods. If domain or
method is hidden, it could make sense to only supply signature with a params
object to make it stable.

[Sami, 2016/04/22 10:36:22]

Great points, I didn't consider that we might add new parameters to events that
currently don't have any. I'll implement your second suggestion in the patch
that adds experimental commands.

+    {% endif %}
+}
+  {% endfor %}
+{% endif %}
 
 }  // namespace {{domain.domain | camelcase_to_hacker_style}}