[Extensions Bindings] Allow custom hooks to return values, throw

extensions/renderer/api_binding_hooks.h

Index: extensions/renderer/api_binding_hooks.h
diff --git a/extensions/renderer/api_binding_hooks.h b/extensions/renderer/api_binding_hooks.h
index d6620275017e656fc0182af51f7fdc2d69d78c12..8abe227661b86f1f8dd390db90e842bfc428f1a1 100644
--- a/extensions/renderer/api_binding_hooks.h
+++ b/extensions/renderer/api_binding_hooks.h
@@ -49,7 +49,8 @@ class APIBindingHooks {
       base::Callback<RequestResult(const APISignature*,
                                    v8::Local<v8::Context> context,
                                    std::vector<v8::Local<v8::Value>>*,
-                                   const ArgumentSpec::RefMap&)>;
+                                   const ArgumentSpec::RefMap&,
+                                   v8::Local<v8::Value>* return_value)>;
 
   explicit APIBindingHooks(const binding::RunJSFunctionSync& run_js);
   ~APIBindingHooks();
@@ -68,14 +69,15 @@ class APIBindingHooks {
                            const std::string& api_name);
 
   // Looks for a custom hook to handle the given request and, if one exists,
-  // runs it. Returns the result of trying to run the hook, or NOT_HANDLED if no
-  // hook was found.
+  // runs it. Returns the result of running the hook, if any. Populates
+  // |return_value| with a value to return, if any.
   RequestResult HandleRequest(const std::string& api_name,
                               const std::string& method_name,
                               v8::Local<v8::Context> context,
                               const APISignature* signature,
                               std::vector<v8::Local<v8::Value>>* arguments,
-                              const ArgumentSpec::RefMap& type_refs);
+                              const ArgumentSpec::RefMap& type_refs,
+                              v8::Local<v8::Value>* return_value);

[jbroman, 2017/01/02 20:05:46]

nit: This argument list is getting a little long. WDYT of at wrapping this up
with the result enum:

struct RequestResult {
  enum ResultCode { HANDLED, INVALID_INVOCATION, ... };
  ResultCode code;
  v8::Local<v8::Value> value;  // if code == HANDLED
};

[Devlin, 2017/01/04 18:38:07]

Hmm... it makes it seem a little more verbose to me, but I don't feel too
strongly.  I've done this in the latest patch - if you prefer it, let's keep it.

 
   // Returns a JS interface that can be used to register hooks.
   v8::Local<v8::Object> GetJSHookInterface(const std::string& api_name,