[runtime] Port simple String.prototype.indexOf cases to TF 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 9877 matching lines @@
 
   static inline Handle<String> Flatten(Handle<String> string,
                                        PretenureFlag pretenure = NOT_TENURED);
 
   // Tries to return the content of a flat string as a structure holding either
   // a flat vector of char or of uc16.
   // If the string isn't flat, and therefore doesn't have flat content, the
   // returned structure will report so, and can't provide a vector of either
   // kind.
   FlatContent GetFlatContent();
+  FlatContent GetFlattenedContent();
 
   // Returns the parent of a sliced string or first part of a flat cons string.
   // Requires: StringShape(this).IsIndirect() && this->IsFlat()
   inline String* GetUnderlying();
 
   // String relational comparison, implemented according to ES6 section 7.2.11
   // Abstract Relational Comparison (step 5): The comparison of Strings uses a
   // simple lexicographic ordering on sequences of code unit values. There is no
   // attempt to use the more complex, semantically oriented definitions of
   // character or string equality and collating order defined in the Unicode
@@ skipping 2082 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_