[analyzer] [NFC] Use StringRef when returning a large string literal in HTMLDiagnostics

[george.karpenkov]

Summary

(NB: could be a clang-tidy / analyzer check)

lib/StaticAnalyzer/Core/HTMLDiagnostics.cpp

public:
   void FinalizeHTML(const PathDiagnostic& D, Rewriter &R,
                     const SourceManager& SMgr, const PathPieces& path,
                     FileID FID, const FileEntry *Entry, const char *declName);
 
   // Rewrite the file specified by FID with HTML formatting.
   void RewriteFile(Rewriter &R, const SourceManager& SMgr,
                    const PathPieces& path, FileID FID);
 
-  /// \return Javascript for navigating the HTML report using j/k keys.
-  std::string generateKeyboardNavigationJavascript();
 
 private:
   /// \return Javascript for displaying shortcuts help;
-  std::string showHelpJavascript();
+  StringRef showHelpJavascript();
+
+  /// \return Javascript for navigating the HTML report using j/k keys.
+  StringRef generateKeyboardNavigationJavascript();
 };
 
 } // namespace
 
 void ento::createHTMLDiagnosticConsumer(AnalyzerOptions &AnalyzerOpts,
                                         PathDiagnosticConsumers &C,
                                         const std::string& prefix,
                                         const Preprocessor &PP) {
// Embed meta-data tags.
 
     // Insert the text.
     R.InsertTextBefore(SMgr.getLocForStartOfFile(FID), os.str());
   }
 
   html::AddHeaderFooterInternalBuiltinCSS(R, FID, Entry->getName());
 }
 
-std::string HTMLDiagnostics::showHelpJavascript() {
+StringRef HTMLDiagnostics::showHelpJavascript() {
   return R"<<<(
 <script type='text/javascript'>
 
 var toggleHelp = function() {
     var hint = document.querySelector("#tooltiphint");
     var attributeName = "hidden";
     if (hint.hasAttribute(attributeName)) {
       hint.removeAttribute(attributeName);
void HTMLDiagnostics::HighlightRange(Rewriter& R, FileID BugFileID,
   // selected range.
 
   SourceLocation E =
     InstantiationEnd.getLocWithOffset(EndColNo - OldEndColNo);
 
   html::HighlightRange(R, InstantiationStart, E, HighlightStart, HighlightEnd);
 }
 
-std::string HTMLDiagnostics::generateKeyboardNavigationJavascript() {
+StringRef HTMLDiagnostics::generateKeyboardNavigationJavascript() {
   return R"<<<(
 <script type='text/javascript'>
 var digitMatcher = new RegExp("[0-9]+");
 
 document.addEventListener("DOMContentLoaded", function() {
     document.querySelectorAll(".PathNav > a").forEach(
         function(currentValue, currentIndex) {
             var hrefValue = currentValue.getAttribute("href");