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

extensions/renderer/api_binding_hooks.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EXTENSIONS_RENDERER_API_BINDING_HOOKS_H_
 #define EXTENSIONS_RENDERER_API_BINDING_HOOKS_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 12 matching lines @@
 class APISignature;
 
 // A class to register custom hooks for given API calls that need different
 // handling. An instance exists for a single API, but can be used across
 // multiple contexts (but only on the same thread).
 // TODO(devlin): We have both C++ and JS custom bindings, but this only allows
 // for registration of C++ handlers. Add JS support.
 class APIBindingHooks {
  public:
   // The result of checking for hooks to handle a request.
-  enum class RequestResult {
-    HANDLED,             // A custom hook handled the request.
-    THROWN,              // An exception was thrown during parsing or handling.
-    INVALID_INVOCATION,  // The request was called with invalid arguments.
-    NOT_HANDLED,         // The request was not handled.
+  struct RequestResult {
+    enum ResultCode {
+      HANDLED,             // A custom hook handled the request.
+      THROWN,              // An exception was thrown during parsing or
+                           // handling.
+      INVALID_INVOCATION,  // The request was called with invalid arguments.
+      NOT_HANDLED,         // The request was not handled.
+    };
+
+    explicit RequestResult(ResultCode code);
+    RequestResult(const RequestResult& other);
+    ~RequestResult();
+
+    ResultCode code;
+    v8::Local<v8::Value> return_value;  // Only valid if code == HANDLED.
   };
 
   // The callback to handle an API method. We pass in the expected signature
   // (so the caller can verify arguments, optionally after modifying/"massaging"
   // them) and the passed arguments. The handler is responsible for returning,
   // which depending on the API could mean either returning synchronously
   // through gin::Arguments::Return or asynchronously through a passed callback.
   // TODO(devlin): As we continue expanding the hooks interface, we should allow
   // handlers to register a request so that they don't have to maintain a
   // reference to the callback themselves.
@@ skipping 13 matching lines @@
   // Registers a JS script to be compiled and run in order to initialize any JS
   // hooks within a v8 context.
   void RegisterJsSource(v8::Global<v8::String> source,
                         v8::Global<v8::String> resource_name);
 
   // Initializes JS hooks within a context.
   void InitializeInContext(v8::Local<v8::Context> context,
                            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.
   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);
 
   // Returns a JS interface that can be used to register hooks.
   v8::Local<v8::Object> GetJSHookInterface(const std::string& api_name,
                                            v8::Local<v8::Context> context);
@@ skipping 22 matching lines @@
   // it's in direct response to JS calling in. There should be no reason that
   // script is disabled.
   binding::RunJSFunctionSync run_js_;
 
   DISALLOW_COPY_AND_ASSIGN(APIBindingHooks);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_API_BINDING_HOOKS_H_