grand PR to port the remaining paths (FieldPath and ResourcePath). (#865)

* naively remove FSTPath import and source/test files.

* port FieldPath, part I

* port FieldPath, part II

* port ResourcePath, part I

* port ResourcePath, part II

* the grand commit to fix build errors

* use testutil:: helper instead of those from FSTHelpers

* fix test and lint

* use c_str in errmsg directly

* fix

* fix

* make code clean

* fix integration test I missed

* fix to avoid naming collision in preprocessor

* address changes

* address changes

* address changes

* fix: fieldMask are actually shared with different context.

* address changes

* address changes

1 files changed, 8 insertions, 0 deletions

diff --git a/Firestore/core/src/firebase/firestore/util/string_apple.h b/Firestore/core/src/firebase/firestore/util/string_apple.h
index 3f6b814..73388be 100644
--- a/Firestore/core/src/firebase/firestore/util/string_apple.h
+++ b/Firestore/core/src/firebase/firestore/util/string_apple.h
@@ -22,6 +22,8 @@
 
 #import <Foundation/Foundation.h>
 
+#include <string>
+
 #include "absl/strings/string_view.h"
 
 namespace firebase {
@@ -57,6 +59,12 @@ inline absl::string_view MakeStringView(NSString* str) {
       [str UTF8String], [str lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
 }
 
+// Creates a std::string wrapper for the contents of the given NSString.
+inline std::string MakeString(NSString* str) {
+  return std::string([str UTF8String],
+                     [str lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
+}
+
 }  // namespace util
 }  // namespace firestore
 }  // namespace firebase