idl: Remove comment about _ in idl identifier

The way to handle '_' in identifier is described Web IDL spec.
We don't need a confusing comment as if it comes from our IDL compiler implementation.
https://heycam.github.io/webidl/#idl-names


Bug: 820353
Change-Id: Iba6c851daa6ae0dc6d690b220a5c757d507e4dc7
Reviewed-on: https://chromium-review.googlesource.com/1092217Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565588}

third_party/blink/renderer/modules/indexeddb/idb_key_range.idl

@@ -41,7 +41,5 @@
                                                                                 optional boolean lowerOpen = false,
                                                                                 optional boolean upperOpen = false);
 
-    // '_' prefix is needed because "includes" is a keyword of Web IDL and our
-    // parser cannot handle a keyword as an identifier. (https://crbug.com/820353)
     [CallWith=ScriptState, RaisesException] boolean _includes(any key);
 };

tools/idl_parser/test_parser/interface_web.idl

@@ -685,7 +685,7 @@ Foo includes Bar;
  *      PrimitiveType(void)
  */
 interface IFaceWithKeyword {
-  // '_' prefix is needed because "includes" is a keyword of Web IDL and our
-  // parser cannot handle a keyword as an identifier. (https://crbug.com/820353)
+  // '_' prefix needs to be removed in tokenization.
+  // https://heycam.github.io/webidl/#idl-names
   void _includes(DOMString val);
 };