[builtins] Move StringIndexOf to a builtin.

src/objects.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 9230 matching lines @@
   // to the Unicode standard could test as unequal. In effect this algorithm
   // assumes that both Strings are already in normalized form. Also, note that
   // for strings containing supplementary characters, lexicographic ordering on
   // sequences of UTF-16 code unit values differs from that on sequences of code
   // point values.
   MUST_USE_RESULT static ComparisonResult Compare(Handle<String> x,
                                                   Handle<String> y);
 
   // Perform string match of pattern on subject, starting at start index.
   // Caller must ensure that 0 <= start_index <= sub->length().
-  static int IndexOf(Isolate* isolate, Handle<String> sub, Handle<String> pat,
-                     int start_index);
+  static Object* IndexOf(Isolate* isolate, Handle<Object> receiver,
+                         Handle<Object> pattern, Handle<Object> position);
 
   static Object* LastIndexOf(Isolate* isolate, Handle<Object> receiver,
                              Handle<Object> search, Handle<Object> position);
 
   // String equality operations.
   inline bool Equals(String* other);
   inline static bool Equals(Handle<String> one, Handle<String> two);
   bool IsUtf8EqualTo(Vector<const char> str, bool allow_prefix_match = false);
   bool IsOneByteEqualTo(Vector<const uint8_t> str);
   bool IsTwoByteEqualTo(Vector<const uc16> str);
@@ skipping 1965 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_