Refactored custom call IC generators:

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index dcfb2eedad09ff06cbcb67bd5da2b65faa0e7183..06b1ca081c3363957a09dacdfa0854b66e17b104 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3200,7 +3200,7 @@ class SharedFunctionInfo: public HeapObject {
 
   // [function data]: This field holds some additional data for function.
   // Currently it either has FunctionTemplateInfo to make benefit the API
-  // or Proxy wrapping CustomCallGenerator.
+  // or Smi identifying a custom call generator.
   // In the long run we don't want all functions to have this field but
   // we can fix that when we have a better model for storing hidden data
   // on objects.
@@ -3209,6 +3209,7 @@ class SharedFunctionInfo: public HeapObject {
   inline bool IsApiFunction();
   inline FunctionTemplateInfo* get_api_func_data();
   inline bool HasCustomCallGenerator();
+  inline int custom_call_generator_id();
 
   // [script info]: Script from which the function originates.
   DECL_ACCESSORS(script, Object)