[FileSystem] Remove Exists() from FileSpec

This patch removes the Exists method from FileSpec and updates its uses
with calls to the FileSystem.

Differential revision: https://reviews.llvm.org/D53845

llvm-svn: 345854
diff --git a/lldb/source/Core/Debugger.cpp b/lldb/source/Core/Debugger.cpp
index a0fc729..5b88246 100644
--- a/lldb/source/Core/Debugger.cpp
+++ b/lldb/source/Core/Debugger.cpp
@@ -656,7 +656,8 @@
   const bool find_other = true;
   char dir_path[PATH_MAX];
   if (FileSpec dir_spec = HostInfo::GetSystemPluginDir()) {
-    if (dir_spec.Exists() && dir_spec.GetPath(dir_path, sizeof(dir_path))) {
+    if (FileSystem::Instance().Exists(dir_spec) &&
+        dir_spec.GetPath(dir_path, sizeof(dir_path))) {
       FileSystem::Instance().EnumerateDirectory(dir_path, find_directories,
                                                 find_files, find_other,
                                                 LoadPluginCallback, this);
@@ -664,7 +665,8 @@
   }
 
   if (FileSpec dir_spec = HostInfo::GetUserPluginDir()) {
-    if (dir_spec.Exists() && dir_spec.GetPath(dir_path, sizeof(dir_path))) {
+    if (FileSystem::Instance().Exists(dir_spec) &&
+        dir_spec.GetPath(dir_path, sizeof(dir_path))) {
       FileSystem::Instance().EnumerateDirectory(dir_path, find_directories,
                                                 find_files, find_other,
                                                 LoadPluginCallback, this);