tools/gn: move the implementation of IsIdentifierXXX functions to the source file

tools/gn/tokenizer.cc

Index: tools/gn/tokenizer.cc
diff --git a/tools/gn/tokenizer.cc b/tools/gn/tokenizer.cc
index db10f6ae094946c11b659aca6dea43f207459f61..4dd71d5beaf953e66acaeb19a7d062270f632ee7 100644
--- a/tools/gn/tokenizer.cc
+++ b/tools/gn/tokenizer.cc
@@ -180,6 +180,16 @@ bool Tokenizer::IsNewline(const base::StringPiece& buffer, size_t offset) {
   return buffer[offset] == '\n';
 }
 
+// static
+bool Tokenizer::IsIdentifierFirstChar(char c) {
+  return base::IsAsciiAlpha(c) || c == '_';
+}
+
+// static
+bool Tokenizer::IsIdentifierContinuingChar(char c) {
+  // Also allow digits after the first char.
+  return IsIdentifierFirstChar(c) || base::IsAsciiDigit(c);
+}
 
 void Tokenizer::AdvanceToNextToken() {
   while (!at_end() && IsCurrentWhitespace())