Add support for .proto files

.proto files are translated to .pb.cc and .pb.h files, which are then
compiled normally.

Bug: 32286026
Test: mmma -j system/extras/perfprofd
Change-Id: I538071424d667aacf35b4b8bfebe217f5f092726
diff --git a/cc/gen.go b/cc/gen.go
index b35eee5..1451895 100644
--- a/cc/gen.go
+++ b/cc/gen.go
@@ -95,6 +95,10 @@
 			cppFile := android.GenPathWithExt(ctx, srcFile, "cpp")
 			srcFiles[i] = cppFile
 			genLex(ctx, srcFile, cppFile)
+		case ".proto":
+			cppFile, headerFile := genProto(ctx, srcFile, buildFlags.protoFlags)
+			srcFiles[i] = cppFile
+			deps = append(deps, headerFile)
 		}
 	}