[Omit needless words] Don't avoid keywords that will be allowed after '.'.

In anticipation of SE-0071, teach the Clang importer to only avoid
dynamicType/self/Protocol/init as base names. Fixes
rdar://problem/25399965.

lib/Basic/StringExtras.cpp

@@ -34,6 +34,16 @@ bool swift::canBeArgumentLabel(StringRef identifier) {
   return true;
 }
 
+bool swift::canBeMemberName(StringRef identifier) {
+  return llvm::StringSwitch<bool>(identifier)
+    .Case("dynamicType", false)
+    .Case("init", false)
+    .Case("Protocol", false)
+    .Case("self", false)
+    .Case("Type", false)
+    .Default(true);
+}
+
 PrepositionKind swift::getPrepositionKind(StringRef word) {
 #define DIRECTIONAL_PREPOSITION(Word)           \
   if (word.equals_lower(#Word))                 \
@@ -334,15 +344,6 @@ size_t camel_case::findWord(StringRef string, StringRef word) {
   }
 }
 
-/// Determine whether the given identifier is a keyword.
-static bool isKeyword(StringRef identifier) {
-  return llvm::StringSwitch<bool>(identifier)
-#define KEYWORD(kw) .Case(#kw, true)
-#define SIL_KEYWORD(kw)
-#include "swift/Parse/Tokens.def"
-    .Default(false);
-}
-
 /// Skip a type suffix that can be dropped.
 static Optional<StringRef> skipTypeSuffix(StringRef typeName) {
   if (typeName.empty()) return None;
@@ -810,9 +811,9 @@ static StringRef omitNeedlessWords(StringRef name,
   case NameRole::BaseName:
   case NameRole::BaseNameSelf:
   case NameRole::Property:
-    // If we ended up with a keyword for a property name or base name,
+    // If we ended up with something that can't be a member name, do nothing.
     // do nothing.
-    if (isKeyword(name))
+    if (!canBeMemberName(name))
       return origName;
 
     // If we ended up with a vacuous name like "get" or "set", do nothing.
@@ -1093,7 +1094,7 @@ static bool splitBaseNameAfterLastPreposition(
   {
     auto newWords = camel_case::getWords(newBaseName);
     auto newWordsIter = newWords.begin();
-    bool isKeyword = ::isKeyword(*newWordsIter);
+    bool isKeyword = !canBeMemberName(*newWordsIter);
     bool isVacuous = isVacuousName(*newWordsIter);
     if (isKeyword || isVacuous) {
       // Just one word?