[llvm-cov] Make a helper method static for re-use (NFC)

llvm-svn: 281876
diff --git a/llvm/tools/llvm-cov/CoverageReport.h b/llvm/tools/llvm-cov/CoverageReport.h
index 7a06954..37bb842 100644
--- a/llvm/tools/llvm-cov/CoverageReport.h
+++ b/llvm/tools/llvm-cov/CoverageReport.h
@@ -35,9 +35,9 @@
   void renderFunctionReports(ArrayRef<StringRef> Files, raw_ostream &OS);
 
   /// Prepare file reports for the files specified in \p Files.
-  std::vector<FileCoverageSummary>
-  prepareFileReports(FileCoverageSummary &Totals,
-                     ArrayRef<StringRef> Files) const;
+  static std::vector<FileCoverageSummary>
+  prepareFileReports(const coverage::CoverageMapping &Coverage,
+                     FileCoverageSummary &Totals, ArrayRef<StringRef> Files);
 
   /// Render file reports for every unique file in the coverage mapping.
   void renderFileReports(raw_ostream &OS) const;