Use the tonic namespace for tonic + resulting build fixes

tonic/dart_builtin.cc

Index: tonic/dart_builtin.cc
diff --git a/tonic/dart_builtin.cc b/tonic/dart_builtin.cc
index 5c4803f08ca74ffd9bc23df5a01f995e98e0d165..1d217cca0c1489755885a558597c21e3b8529751 100644
--- a/tonic/dart_builtin.cc
+++ b/tonic/dart_builtin.cc
@@ -10,7 +10,7 @@
 #include "base/logging.h"
 #include "tonic/dart_converter.h"
 
-namespace blink {
+namespace tonic {
 
 DartBuiltin::DartBuiltin(const Natives* natives, size_t count)
     : natives_(natives), count_(count) {
@@ -53,4 +53,4 @@ Dart_Handle DartBuiltin::LookupLibrary(const char* name) {
     return library;
 }
 
-}  // namespace blink
+}  // namespace tonic