[Omit needless words] Don't split "PlugIn".

Fixes rdar://problem/26334014.

Author: DougGregor

lib/Basic/StringExtras.cpp

@@ -886,6 +886,10 @@ camel_case::toLowercaseInitialisms(StringRef string,
 /// splitting.
 static bool wordConflictsBeforePreposition(StringRef word,
                                            StringRef preposition) {
+  if (camel_case::sameWordIgnoreFirstCase(preposition, "in") &&
+      camel_case::sameWordIgnoreFirstCase(word, "plug"))
+    return true;
+
   return false;
 }
 

test/IDE/Inputs/custom-modules/OmitNeedlessWords.h

@@ -34,6 +34,7 @@
 -(void)doSomethingSeparatedBy:(NSInteger)value;
 +(nonnull OmitNeedlessWords *)currentOmitNeedlessWords;
 +(void)setCurrentOmitNeedlessWords:(nonnull OmitNeedlessWords *)value;
+-(void)compilerPlugInValue:(NSInteger)value;
 @end
 
 @interface ABCDoodle : NSObject

test/IDE/print_omit_needless_words.swift

@@ -308,6 +308,9 @@
 // CHECK-OMIT-NEEDLESS-WORDS: class func current() -> OmitNeedlessWords
 // CHECK-OMIT-NEEDLESS-WORDS: class func setCurrent(_: OmitNeedlessWords)
 
+// Don't split "PlugIn".
+// CHECK-OMIT-NEEDLESS-WORDS: func compilerPlugInValue(_: Int)
+
 // Property-name sensitivity in the base name "Self" stripping.
 // CHECK-OMIT-NEEDLESS-WORDS: func addDoodle(_: ABCDoodle)