Fix window.history.go() with no parameter.

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index ca23114424b25110cd961183512fc18ee9f53b60..cff662181169824c51ec832b6ec7aa8ff486880a 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -3084,8 +3084,15 @@ - (BOOL)handleWindowHistoryForwardMessage:(base::DictionaryValue*)message
 
 - (BOOL)handleWindowHistoryGoMessage:(base::DictionaryValue*)message
                              context:(NSDictionary*)context {
+  std::string valueKey = "value";
+  if (!message->HasKey(valueKey)) {
+    // window.history.go() with no input parameter should behave as

[Eugene But (OOO till 7-30), 2016/12/09 22:58:19]

Should we fix this in JS as follows?:

|invokeOnHost_({'command': 'window.history.go', 'value': delta | 0});|

[kkhorimoto, 2016/12/13 00:30:56]

Done.

+    // window.history.go(0).
+    [self goDelta:0];
+    return YES;
+  }
   int delta = 0;
-  if (message->GetInteger("value", &delta)) {
+  if (message->GetInteger(valueKey, &delta)) {
     [self goDelta:delta];
     return YES;
   }