reduce allocation on checking DOM attributes and do not hard-code number of elements of array constant

`to_lower` allocates new string but the allocation is not necessary
here.

src/html.rs

@@ -12,7 +12,7 @@ use std::collections::HashMap;
 use std::default::Default;
 use utils::{data_to_dataurl, is_valid_url, resolve_css_imports, resolve_url, url_has_protocol};
 
-const ICON_VALUES: [&str; 5] = [
+const ICON_VALUES: &[&str] = &[
     "icon",
     "shortcut icon",
     "mask-icon",
@@ -37,7 +37,10 @@ pub fn get_node_name(node: &Handle) -> String {
 }
 
 pub fn is_icon(attr_value: &str) -> bool {
-    ICON_VALUES.contains(&&*attr_value.to_lowercase())
+    ICON_VALUES
+        .iter()
+        .find(|a| attr_value.eq_ignore_ascii_case(a))
+        .is_some()
 }
 
 pub fn walk_and_embed_assets(

src/js.rs

@@ -1,4 +1,4 @@
-const JS_DOM_EVENT_ATTRS: [&str; 21] = [
+const JS_DOM_EVENT_ATTRS: &[&str] = &[
     // Input
     "onfocus",
     "onblur",
@@ -28,5 +28,8 @@ const JS_DOM_EVENT_ATTRS: [&str; 21] = [
 
 // Returns true if DOM attribute name matches a native JavaScript event handler
 pub fn attr_is_event_handler(attr_name: &str) -> bool {
-    JS_DOM_EVENT_ATTRS.contains(&attr_name.to_lowercase().as_str())
+    JS_DOM_EVENT_ATTRS
+        .iter()
+        .find(|a| attr_name.eq_ignore_ascii_case(a))
+        .is_some()
 }