Add some simple HTMLViewer apptests.

mojo/application/application_test_main_chromium.cc

Index: mojo/application/application_test_main_chromium.cc
diff --git a/mojo/application/application_test_main_chromium.cc b/mojo/application/application_test_main_chromium.cc
index e6df84fac7af67f54bb1689a3d421471123241bf..4ce761a8a36ffa7a741c862cc82623a30a6f2c7e 100644
--- a/mojo/application/application_test_main_chromium.cc
+++ b/mojo/application/application_test_main_chromium.cc
@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 #include "base/at_exit.h"
+#include "base/command_line.h"
+#include "base/test/test_timeouts.h"
 #include "mojo/public/c/system/main.h"
 #include "mojo/public/cpp/application/application_test_base.h"
 
@@ -10,5 +12,10 @@ MojoResult MojoMain(MojoHandle handle) {
   // An AtExitManager instance is needed to construct message loops.
   base::AtExitManager at_exit;
 
+  // Initialize test timeouts, which requires CommandLine::ForCurrentProcess().
+  // TODO(msw): Plumb relevant command line args before initializing timeouts.
+  base::CommandLine::Init(0, nullptr);
+  TestTimeouts::Initialize();
+
   return mojo::test::RunAllTests(handle);
 }