[builtins] Move StringIndexOf to a C++ 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 9311 matching lines @@
   // character or string equality and collating order defined in the Unicode
   // specification. Therefore String values that are canonically equal according
   // 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 ES6 21.1.3.8, including checking arguments.
+  static Object* IndexOf(Isolate* isolate, Handle<Object> receiver,
+                                  Handle<Object> search,
+                                  Handle<Object> position);
   // 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);
+  // Caller must ensure that 0 <= start_index <= sub->length(), as this does not
+  // check any arguments.
+  static int IndexOf(Isolate* isolate, Handle<String> receiver,

[Franzi, 2016/09/23 11:37:00]

Is the inner function only used inside Object* IndexOf()? Then I'd prefer a
helper function in an anonymous namespace. 

+                     Handle<String> search, int start_index);
 
   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_