De-ASTContext-ify DeclContext.

Remove ASTContext parameter from DeclContext's methods. This change cascaded down to other Decl's methods and changes to call sites started "escalating".
Timings using pre-tokenized "cocoa.h" showed only a ~1% increase in time run between and after this commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@74506 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/PCHWriter.cpp b/lib/Frontend/PCHWriter.cpp
index e93219e..41a5025 100644
--- a/lib/Frontend/PCHWriter.cpp
+++ b/lib/Frontend/PCHWriter.cpp
@@ -1064,14 +1064,13 @@
 /// bistream, or 0 if no block was written.
 uint64_t PCHWriter::WriteDeclContextLexicalBlock(ASTContext &Context, 
                                                  DeclContext *DC) {
-  if (DC->decls_empty(Context))
+  if (DC->decls_empty())
     return 0;
 
   uint64_t Offset = Stream.GetCurrentBitNo();
   RecordData Record;
-  for (DeclContext::decl_iterator D = DC->decls_begin(Context),
-                               DEnd = DC->decls_end(Context);
-       D != DEnd; ++D)
+  for (DeclContext::decl_iterator D = DC->decls_begin(), DEnd = DC->decls_end();
+         D != DEnd; ++D)
     AddDeclRef(*D, Record);
 
   ++NumLexicalDeclContexts;
@@ -1097,7 +1096,7 @@
     return 0;
 
   // Force the DeclContext to build a its name-lookup table.
-  DC->lookup(Context, DeclarationName());
+  DC->lookup(DeclarationName());
 
   // Serialize the contents of the mapping used for lookup. Note that,
   // although we have two very different code paths, the serialized