[GN] Remove a duplication of a source type check

There was a duplication of the source type checking. It may lead
errors when a type set will be changed for a language.

R=dpranke@chromium.org

Bug: None
Change-Id: Ieab8885899446e625cfe20c1650418a085b937ee
Reviewed-on: https://chromium-review.googlesource.com/702414Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506763}

tools/gn/xcode_object.cc

@@ -13,6 +13,8 @@
 #include "base/memory/ptr_util.h"
 #include "base/strings/string_util.h"
 #include "tools/gn/filesystem_utils.h"
+#include "tools/gn/source_file.h"
+#include "tools/gn/source_file_type.h"
 
 // Helper methods -------------------------------------------------------------
 
@@ -153,9 +155,10 @@ bool HasExplicitFileType(const base::StringPiece& ext) {
   return ext == "dart";
 }
 
-bool IsSourceFileForIndexing(const base::StringPiece& ext) {
-  return ext == "c" || ext == "cc" || ext == "cpp" || ext == "cxx" ||
-         ext == "m" || ext == "mm";
+bool IsSourceFileForIndexing(const SourceFile& src) {
+  const SourceFileType type = GetSourceFileType(src);
+  return type == SOURCE_C || type == SOURCE_CPP || type == SOURCE_M ||
+         type == SOURCE_MM;
 }
 
 void PrintValue(std::ostream& out, IndentRules rules, unsigned value) {
@@ -692,8 +695,7 @@ void PBXProject::AddSourceFile(const std::string& navigator_path,
                                PBXNativeTarget* target) {
   PBXFileReference* file_reference =
       sources_->AddSourceFile(navigator_path, source_path);
-  base::StringPiece ext = FindExtension(&source_path);
-  if (!IsSourceFileForIndexing(ext))
+  if (!IsSourceFileForIndexing(SourceFile(source_path)))
     return;
 
   DCHECK(target);