Use the tonic namespace for tonic + resulting build fixes

tonic/dart_invoke.cc

Index: tonic/dart_invoke.cc
diff --git a/tonic/dart_invoke.cc b/tonic/dart_invoke.cc
index e0dd17456dec7431b2103d7af70256b21cab3056..c76cbcb0c92f80330f9f28f6419b0b3c3e6a7d82 100644
--- a/tonic/dart_invoke.cc
+++ b/tonic/dart_invoke.cc
@@ -8,7 +8,7 @@
 #include "base/trace_event/trace_event.h"
 #include "tonic/dart_error.h"
 
-namespace blink {
+namespace tonic {
 
 bool DartInvokeAppField(Dart_Handle target, Dart_Handle name,
                                int number_of_arguments,
@@ -25,4 +25,4 @@ bool DartInvokeAppClosure(Dart_Handle closure,
       Dart_InvokeClosure(closure, number_of_arguments, arguments));
 }
 
-}  // namespace blink
+}  // namespace tonic