[Extensions Binding] Allow for registering custom hooks

extensions/renderer/api_bindings_system.cc

Index: extensions/renderer/api_bindings_system.cc
diff --git a/extensions/renderer/api_bindings_system.cc b/extensions/renderer/api_bindings_system.cc
index 14ec34115f61085598c5fd4f22f26c85fbd3bb00..9abc8dc37b3f5ee05ce3528e11be172ee320eb0e 100644
--- a/extensions/renderer/api_bindings_system.cc
+++ b/extensions/renderer/api_bindings_system.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
 #include "base/values.h"
+#include "extensions/renderer/api_binding_hooks.h"
 
 namespace extensions {
 
@@ -47,10 +48,20 @@ std::unique_ptr<APIBinding> APIBindingsSystem::CreateNewAPIBinding(
   const base::ListValue* event_definitions = nullptr;
   api_schema.GetList("events", &event_definitions);
 
+  // Find the hooks for the API. If none are registered, we create one.

[jbroman, 2016/12/08 16:58:56]

nit: Is there a need to heap-allocate one when we know it will forever remain
empty?

[Devlin, 2016/12/08 19:12:03]

Mostly just because I didn't want to have to nullcheck in the APIBinding, but
that's not a very compelling reason. :)  Removed the allocation.

+  std::unique_ptr<APIBindingHooks> hooks;
+  auto iter = binding_hooks_.find(api_name);
+  if (iter != binding_hooks_.end()) {
+    hooks = std::move(iter->second);
+    binding_hooks_.erase(iter);
+  } else {
+    hooks = base::MakeUnique<APIBindingHooks>(api_name);
+  }
+
   return base::MakeUnique<APIBinding>(
       api_name, *function_definitions, type_definitions, event_definitions,
       base::Bind(&APIBindingsSystem::OnAPICall, base::Unretained(this)),
-      &type_reference_map_);
+      std::move(hooks), &type_reference_map_);
 }
 
 void APIBindingsSystem::CompleteRequest(int request_id,
@@ -64,6 +75,19 @@ void APIBindingsSystem::FireEventInContext(const std::string& event_name,
   event_handler_.FireEventInContext(event_name, context, response);
 }
 
+APIBindingHooks* APIBindingsSystem::GetHooksForAPI(
+    const std::string& api_name) {
+  DCHECK(api_bindings_.empty())
+      << "Hook registration must happen before creating any binding instances.";
+  auto iter = binding_hooks_.find(api_name);

[jbroman, 2016/12/08 16:58:56]

super-duper-nit: This can be written without doing two map lookups in the new
case (it also winds up a little shorter):

std::unique_ptr<APIBindingHooks>& hooks = binding_hooks_[api_name];
if (!hooks)
  hooks = base::MakeUnique<APIBindingHooks>(api_name);
return hooks.get();

[Devlin, 2016/12/08 19:12:03]

I like it, done.

+  if (iter != binding_hooks_.end())
+    return iter->second.get();
+  auto hooks = base::MakeUnique<APIBindingHooks>(api_name);
+  APIBindingHooks* hooks_weak = hooks.get();
+  binding_hooks_[api_name] = std::move(hooks);
+  return hooks_weak;
+}
+
 void APIBindingsSystem::OnAPICall(const std::string& name,
                                   std::unique_ptr<base::ListValue> arguments,
                                   v8::Isolate* isolate,