Apply snake_case to EventAliases.json5.

The new name is event_interface_aliases.json5 to make sure that it's not
for event type names.

This CL has no behavior changes.

Bug: 770603
Change-Id: I53fb2ab332ed004296dcfa7f70d5504deef14b43
Reviewed-on: https://chromium-review.googlesource.com/965681Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543623}

third_party/WebKit/Source/core/BUILD.gn

@@ -1256,7 +1256,7 @@ process_json5_files("make_core_generated_svg_element_type_helpers") {
 make_event_factory("make_core_generated_event_factory") {
   in_files = [
     "$blink_core_output_dir/event_names.json5",
-    "events/EventAliases.json5",
+    "events/event_interface_aliases.json5",
   ]
   outputs = [
     "$blink_core_output_dir/event_factory.cc",

third_party/WebKit/Source/core/events/EventAliases.json5 → third_party/WebKit/Source/core/events/event_interface_aliases.json5

 {
+  // Aliases for event interface names. They can be used for
+  // document.createEvent() argument.
+  // https://dom.spec.whatwg.org/#dom-document-createevent
   data: [
-    // Aliases
     {
       name: "WebKitAnimationEvent",
       ImplementedAs: "AnimationEvent",