Check NaCl debug mask (not just flag) before choosing PNaCl debug URL.

chrome/test/data/nacl/pnacl_debug_url/pnacl_debug_url.html

Index: chrome/test/data/nacl/pnacl_debug_url/pnacl_debug_url.html
diff --git a/chrome/test/data/nacl/pnacl_debug_url/pnacl_debug_url.html b/chrome/test/data/nacl/pnacl_debug_url/pnacl_debug_url.html
index 7702afca9ccc67807a029d7a71ecbb319b9aea28..a24eb3eb80dcaa2cf024729282b7b3ebc2a9ec06 100644
--- a/chrome/test/data/nacl/pnacl_debug_url/pnacl_debug_url.html
+++ b/chrome/test/data/nacl/pnacl_debug_url/pnacl_debug_url.html
@@ -20,10 +20,14 @@ function create(nmf_url) {
   embed.type = "application/x-pnacl";
   embed.addEventListener("load", function(evt) {
     load_util.shutdown("1 test passed.", true);
+    // Remove the embed so that the debugger will shut down.
+    embed.parentNode.removeChild(embed);

[bradn, 2014/03/27 16:57:14]

FWIW I've observed that the debug stub ends up keeping these alive if they're in
a suspended state.

   }, true);
   embed.addEventListener("error", function(evt) {
     load_util.log("Load error: " + embed.lastError);
     load_util.shutdown("1 test failed.", false);
+    // Remove the embed so that the debugger will shut down.
+    embed.parentNode.removeChild(embed);
   }, true);
   document.body.appendChild(embed);
 }