Revert "Delete Filesystem::TempFilename."

This reverts commit 6de95f06d0512049553f8120547ab78675e3a76a.

Reason for revert: Broke internal projects.
Original change's description:
> Delete Filesystem::TempFilename.
> 
> Also delete a few unused private members of UnixFilesystem.
> 
> Bug: webrtc:6424
> Change-Id: Ib52f2d877690159d197fe767fd04a0d1ade7eb1a
> Reviewed-on: https://webrtc-review.googlesource.com/30301
> Commit-Queue: Taylor Brandstetter <deadbeef@webrtc.org>
> Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#21148}

TBR=deadbeef@webrtc.org,nisse@webrtc.org

Change-Id: I02874f80dbfcafc26dadbb5897e510613801713d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:6424
Reviewed-on: https://webrtc-review.googlesource.com/31160
Reviewed-by: Zhi Huang <zhihuang@webrtc.org>
Commit-Queue: Zhi Huang <zhihuang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21152}

rtc_base/fileutils.h

@@ -94,6 +94,9 @@ class FilesystemInterface {
   // Returns true if pathname refers to a file
   virtual bool IsFile(const Pathname& pathname) = 0;
 
+  virtual std::string TempFilename(const Pathname &dir,
+                                   const std::string &prefix) = 0;
+
   // Determines the size of the file indicated by path.
   virtual bool GetFileSize(const Pathname& path, size_t* size) = 0;
 };
@@ -132,6 +135,11 @@ class Filesystem {
     return EnsureDefaultFilesystem()->IsFile(pathname);
   }
 
+  static std::string TempFilename(const Pathname &dir,
+                                  const std::string &prefix) {
+    return EnsureDefaultFilesystem()->TempFilename(dir, prefix);
+  }
+
   static bool GetFileSize(const Pathname& path, size_t* size) {
     return EnsureDefaultFilesystem()->GetFileSize(path, size);
   }

rtc_base/unixfilesystem.cc

@@ -67,6 +67,22 @@ bool UnixFilesystem::DeleteFile(const Pathname &filename) {
   return ::unlink(filename.pathname().c_str()) == 0;
 }
 
+std::string UnixFilesystem::TempFilename(const Pathname &dir,
+                                         const std::string &prefix) {
+  int len = dir.pathname().size() + prefix.size() + 2 + 6;
+  char *tempname = new char[len];
+
+  snprintf(tempname, len, "%s/%sXXXXXX", dir.pathname().c_str(),
+           prefix.c_str());
+  int fd = ::mkstemp(tempname);
+  if (fd != -1)
+    ::close(fd);
+  std::string ret(tempname);
+  delete[] tempname;
+
+  return ret;
+}
+
 bool UnixFilesystem::MoveFile(const Pathname &old_path,
                               const Pathname &new_path) {
   if (!IsFile(old_path)) {
@@ -103,6 +119,18 @@ bool UnixFilesystem::GetFileSize(const Pathname& pathname, size_t *size) {
   return true;
 }
 
+char* UnixFilesystem::CopyString(const std::string& str) {
+  size_t size = str.length() + 1;
+
+  char* buf = new char[size];
+  if (!buf) {
+    return nullptr;
+  }
+
+  strcpyn(buf, size, str.c_str());
+  return buf;
+}
+
 }  // namespace rtc
 
 #if defined(__native_client__)

rtc_base/unixfilesystem.h

@@ -37,7 +37,20 @@ class UnixFilesystem : public FilesystemInterface {
   // Returns true of pathname represents an existing file
   bool IsFile(const Pathname& pathname) override;
 
+  std::string TempFilename(const Pathname& dir,
+                           const std::string& prefix) override;
+
   bool GetFileSize(const Pathname& path, size_t* size) override;
+
+ private:
+#if defined(WEBRTC_ANDROID) || defined(WEBRTC_MAC)
+  static char* provided_app_data_folder_;
+  static char* provided_app_temp_folder_;
+#else
+  static char* app_temp_path_;
+#endif
+
+  static char* CopyString(const std::string& str);
 };
 
 }  // namespace rtc

rtc_base/win32filesystem.cc

@@ -42,6 +42,16 @@ bool Win32Filesystem::DeleteFile(const Pathname &filename) {
   return ::DeleteFile(ToUtf16(filename.pathname()).c_str()) != 0;
 }
 
+std::string Win32Filesystem::TempFilename(const Pathname &dir,
+                                          const std::string &prefix) {
+  wchar_t filename[MAX_PATH];
+  if (::GetTempFileName(ToUtf16(dir.pathname()).c_str(),
+                        ToUtf16(prefix).c_str(), 0, filename) != 0)
+    return ToUtf8(filename);
+  RTC_NOTREACHED();
+  return "";
+}
+
 bool Win32Filesystem::MoveFile(const Pathname &old_path,
                                const Pathname &new_path) {
   if (!IsFile(old_path)) {

rtc_base/win32filesystem.h

@@ -33,6 +33,14 @@ class Win32Filesystem : public FilesystemInterface {
   // Returns true if a file exists at path
   bool IsFile(const Pathname& path) override;
 
+  // All of the following functions set pathname and return true if successful.
+  // Returned paths always include a trailing backslash.
+  // If create is true, the path will be recursively created.
+  // If append is non-null, it will be appended (and possibly created).
+
+  std::string TempFilename(const Pathname& dir,
+                           const std::string& prefix) override;
+
   bool GetFileSize(const Pathname& path, size_t* size) override;
 };