CallSiteItem getCallSiteItem(CstCallSite callSite) {
    if (callSite == null) {
      throw new NullPointerException("callSite == null");
    }
    return callSites.get(callSite);
  }
Gets the DEX file representation of a call site associated with a call site constant.

<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
@return {@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