Add support for writing unit tests for Mojo-backed apps/extensions APIs.

extensions/test/extensions_unittests_main.cc

Index: extensions/test/extensions_unittests_main.cc
diff --git a/extensions/test/extensions_unittests_main.cc b/extensions/test/extensions_unittests_main.cc
index b13ce80f3c20a1be1843e207803d83e7e2135f78..be46e857c73c541e8e2bf8162332616ad5ec1e73 100644
--- a/extensions/test/extensions_unittests_main.cc
+++ b/extensions/test/extensions_unittests_main.cc
@@ -13,6 +13,7 @@
 #include "extensions/common/constants.h"
 #include "extensions/common/extension_paths.h"
 #include "extensions/test/test_extensions_client.h"
+#include "mojo/embedder/embedder.h"
 #include "ui/base/resource/resource_bundle.h"
 
 namespace {
@@ -96,6 +97,7 @@ void ExtensionsTestSuite::Shutdown() {
 int main(int argc, char** argv) {
   content::UnitTestTestSuite test_suite(new ExtensionsTestSuite(argc, argv));
 
+  mojo::embedder::Init();
   return base::LaunchUnitTests(argc,
                                argv,
                                base::Bind(&content::UnitTestTestSuite::Run,