clang-format: [JS] treat forwardDeclare as an import/export statement.

[djasper]

LG. Submitted as r261528.

lib/Format/TokenAnnotator.cpp

private:
   bool isImportStatement(const FormatToken &Tok) {
     // FIXME: Closure-library specific stuff should not be hard-coded but be
     // configurable.
     return Style.Language == FormatStyle::LK_JavaScript &&
            Tok.TokenText == "goog" && Tok.Next && Tok.Next->is(tok::period) &&
            Tok.Next->Next && (Tok.Next->Next->TokenText == "module" ||
                               Tok.Next->Next->TokenText == "provide" ||
                               Tok.Next->Next->TokenText == "require" ||
-                              Tok.Next->Next->TokenText == "setTestOnly") &&
+                              Tok.Next->Next->TokenText == "setTestOnly" ||
+                              Tok.Next->Next->TokenText == "forwardDeclare") &&
            Tok.Next->Next->Next && Tok.Next->Next->Next->is(tok::l_paren);
   }
 
   void resetTokenMetadata(FormatToken *Token) {
     if (!Token)
       return;
 
     // Reset token type in case we have already looked at it and then

unittests/Format/FormatTestJS.cpp

TEST_F(FormatTestJS, GoogModules) {
   verifyFormat("goog.require('this.is.really.absurdly.long');",
                getGoogleJSStyleWithColumns(40));
   verifyFormat("goog.provide('this.is.really.absurdly.long');",
                getGoogleJSStyleWithColumns(40));
   verifyFormat("var long = goog.require('this.is.really.absurdly.long');",
                getGoogleJSStyleWithColumns(40));
   verifyFormat("goog.setTestOnly('this.is.really.absurdly.long');",
                getGoogleJSStyleWithColumns(40));
+  verifyFormat("goog.forwardDeclare('this.is.really.absurdly.long');",
+               getGoogleJSStyleWithColumns(40));
 
   // These should be wrapped normally.
   verifyFormat(
       "var MyLongClassName =\n"
       "    goog.module.get('my.long.module.name.followedBy.MyLongClassName');");
 }
 
 TEST_F(FormatTestJS, FormatsFreestandingFunctions) {