Get rid of multiple-definition of kInvalidInstance in protozero

This seems to be a blocker for jumbo builds in chromium.
Fix seems pretty straightforward, not sure why kInvalidField
was introduced in the first place.

Bug: crbug.com/863831
Change-Id: I72bb6fed7fd43e68793f2bbacf146246225c7d52
diff --git a/Android.bp b/Android.bp
index 10f63b1..e3e4fbe 100644
--- a/Android.bp
+++ b/Android.bp
@@ -51,6 +51,7 @@
     "src/protozero/message.cc",
     "src/protozero/message_handle.cc",
     "src/protozero/proto_decoder.cc",
+    "src/protozero/proto_field_descriptor.cc",
     "src/protozero/proto_utils.cc",
     "src/protozero/scattered_stream_null_delegate.cc",
     "src/protozero/scattered_stream_writer.cc",
@@ -169,6 +170,7 @@
     "src/protozero/message.cc",
     "src/protozero/message_handle.cc",
     "src/protozero/proto_decoder.cc",
+    "src/protozero/proto_field_descriptor.cc",
     "src/protozero/proto_utils.cc",
     "src/protozero/scattered_stream_null_delegate.cc",
     "src/protozero/scattered_stream_writer.cc",
@@ -302,6 +304,7 @@
     "src/protozero/message.cc",
     "src/protozero/message_handle.cc",
     "src/protozero/proto_decoder.cc",
+    "src/protozero/proto_field_descriptor.cc",
     "src/protozero/proto_utils.cc",
     "src/protozero/scattered_stream_delegate_for_testing.cc",
     "src/protozero/scattered_stream_null_delegate.cc",
@@ -3485,6 +3488,7 @@
     "src/protozero/message.cc",
     "src/protozero/message_handle.cc",
     "src/protozero/proto_decoder.cc",
+    "src/protozero/proto_field_descriptor.cc",
     "src/protozero/proto_utils.cc",
     "src/protozero/scattered_stream_null_delegate.cc",
     "src/protozero/scattered_stream_writer.cc",
@@ -3684,6 +3688,7 @@
     "src/protozero/message_unittest.cc",
     "src/protozero/proto_decoder.cc",
     "src/protozero/proto_decoder_unittest.cc",
+    "src/protozero/proto_field_descriptor.cc",
     "src/protozero/proto_utils.cc",
     "src/protozero/proto_utils_unittest.cc",
     "src/protozero/scattered_stream_delegate_for_testing.cc",