[Extensions Bindings] Add errors to signature parsing

extensions/renderer/argument_spec.cc

Index: extensions/renderer/argument_spec.cc
diff --git a/extensions/renderer/argument_spec.cc b/extensions/renderer/argument_spec.cc
index 08768595b80ddb9dbb27efc8bf4eaa1b42138af0..9bdefdb4c7ef79208f0cdc36a3fc8c4c29f84c07 100644
--- a/extensions/renderer/argument_spec.cc
+++ b/extensions/renderer/argument_spec.cc
@@ -420,8 +420,16 @@ bool ArgumentSpec::ParseArgumentToObject(
     // HasOwnProperty() check here in the future, if we desire.
     // See also comment in ParseArgumentToArray() about passing in custom
     // crazy values here.
-    if (!object->Get(context, key).ToLocal(&prop_value))
+    if (!object->Get(context, key).ToLocal(&prop_value)) {
+      // Technically, in the case of the property being removed before access,

[jbroman, 2017/04/27 19:37:20]

Hmm? Getting a nonexistent property will successfully produce undefined. This
branch is only for cases where some exception happened (either deliberated by
script, or due to another issue like an access check).

[Devlin, 2017/05/01 22:22:09]

Ah, good point.  Comment removed.

+      // this error message will be wrong. But since that can only happen if
+      // someone removes a property after the initial GetOwnPropertyNames()
+      // check, this seems reasonable enough - these error messages are meant
+      // to be helpful, but don't need 100% accuracy in deliberately-crazy
+      // cases.
+      *error = api_errors::ScriptThrewError();
       return false;
+    }
 
     // Note: We don't serialize undefined or null values.
     // TODO(devlin): This matches current behavior, but it is correct?