Test and fix writing wide chars.

format.h

@@ -1023,7 +1023,7 @@ class BasicFormatter {
     Arg(double value) : type(DOUBLE), double_value(value), formatter(0) {}
     Arg(long double value)
     : type(LONG_DOUBLE), long_double_value(value), formatter(0) {}
-    Arg(char value) : type(CHAR), int_value(value), formatter(0) {}
+    Arg(Char value) : type(CHAR), int_value(value), formatter(0) {}
 
     Arg(const Char *value) : type(STRING), formatter(0) {
       string.value = value;

format_test.cc

@@ -1032,6 +1032,7 @@ TEST(FormatterTest, WideFormatString) {
   EXPECT_EQ(L"42", str(Format(L"{}") << 42));
   EXPECT_EQ(L"4.2", str(Format(L"{}") << 4.2));
   EXPECT_EQ(L"abc", str(Format(L"{}") << L"abc"));
+  EXPECT_EQ(L"z", str(Format(L"{}") << L'z'));
 }
 
 TEST(FormatterTest, FormatStringFromSpeedTest) {