protogen: camel-case "Foo.bar" as "FooBar" instead of "Foo_Bar".

Given:

  message Parent {
    message Child1 {}
    message child2 {}
  }

Historic behavior is to generate child messages named:

  Parent_Child1
  ParentChild2

Avoid adding an _ in the latter case.

Change-Id: I49a6732655d64967b8c7bb7ad358ae54d294f7b4
Reviewed-on: https://go-review.googlesource.com/c/140898
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/protogen/names.go b/protogen/names.go
index 445613f..9da11d9 100644
--- a/protogen/names.go
+++ b/protogen/names.go
@@ -136,6 +136,8 @@
 	for ; i < len(s); i++ {
 		c := s[i]
 		switch {
+		case c == '.' && i+1 < len(s) && isASCIILower(s[i+1]):
+			// Skip over .<lowercase>, to match historic behavior.
 		case c == '.':
 			t = append(t, '_') // Convert . to _.
 		case c == '_' && (i == 0 || s[i-1] == '.'):