Use JS String includes/startsWith/endsWith (#10170)

Even when completely inlined, should produce smaller code than the
previous emulation, and depending on the browser implementation this
could perform slightly better as well.

Author: niloc132

user/super/com/google/gwt/emul/java/lang/String.java

@@ -399,7 +399,7 @@ public String concat(String str) {
   }
 
   public boolean contains(CharSequence s) {
-    return indexOf(s.toString()) != -1;
+    return asNativeString().includes(s.toString());
   }
 
   public boolean contentEquals(CharSequence cs) {
@@ -411,9 +411,7 @@ public boolean contentEquals(StringBuffer sb) {
   }
 
   public boolean endsWith(String suffix) {
-    // If IE8 supported negative start index, we could have just used "-suffixlength".
-    int suffixlength = suffix.length();
-    return asNativeString().substr(length() - suffixlength, suffixlength).equals(suffix);
+    return asNativeString().endsWith(suffix);
   }
 
   // Marked with @DoNotInline because we don't have static eval for "==" yet.
@@ -691,11 +689,11 @@ public String[] split(String regex, int maxMatch) {
   }
 
   public boolean startsWith(String prefix) {
-    return startsWith(prefix, 0);
+    return asNativeString().startsWith(prefix);
   }
 
   public boolean startsWith(String prefix, int toffset) {
-    return toffset >= 0 && asNativeString().substr(toffset, prefix.length()).equals(prefix);
+    return asNativeString().startsWith(prefix, toffset);
   }
 
   @Override
@@ -991,11 +989,16 @@ private static class NativeString {
     public static native String fromCharCode(char x);
     public int length;
     public native char charCodeAt(int index);
+    public native boolean endsWith(String suffix);
     public native int indexOf(String str);
     public native int indexOf(String str, int startIndex);
+    public native boolean includes(String str);
+    public native boolean includes(String str, int startIndex);
     public native int lastIndexOf(String str);
     public native int lastIndexOf(String str, int start);
     public native String replace(NativeRegExp regex, String replace);
+    public native boolean startsWith(String prefix);
+    public native boolean startsWith(String prefix, int toffset);
     public native String substr(int beginIndex);
     public native String substr(int beginIndex, int len);
     public native String toLocaleLowerCase();