void addCallSiteItem(CstCallSite callSite, CallSiteItem callSiteItem) {
    if (callSite == null) {
      throw new NullPointerException("callSite == null");
    }
    if (callSiteItem == null) {
      throw new NullPointerException("callSiteItem == null");
    }
    callSites.put(callSite, callSiteItem);
  }
Adds an association between call site constant and its DEX file representation.

<p>This method is not synchronized as it is called during DEX file writing which happens
concurrently on a per DEX file basis and this information per DEX file.

@param callSite {@code non-null;} a constant call site
@param callSiteItem {@code non-null;} a call site item as represented in a DEX file
android/android_framework/dex-maker/src/main/java/com/android/dx/dex/file/CallSiteIdsSection.java