Don't crash in ~HostNPScriptObject() when the object wasn't initialized.

remoting/host/chromoting_host_context.cc

Index: remoting/host/chromoting_host_context.cc
diff --git a/remoting/host/chromoting_host_context.cc b/remoting/host/chromoting_host_context.cc
index 6f029438be2c5459c1bf0b098d054ba3db855087..b18cd9ea9382ee45c2aae4e24cda90534ccaf11b 100644
--- a/remoting/host/chromoting_host_context.cc
+++ b/remoting/host/chromoting_host_context.cc
@@ -23,12 +23,10 @@ ChromotingHostContext::ChromotingHostContext(
 ChromotingHostContext::~ChromotingHostContext() {
 }
 
-void ChromotingHostContext::Start() {
+bool ChromotingHostContext::Start() {
   // Start all the threads.
-  main_thread_.Start();
-  encode_thread_.Start();
-  jingle_thread_.Start();
-  desktop_thread_.Start();
+  return main_thread_.Start() && encode_thread_.Start() &&
+      jingle_thread_.Start() && desktop_thread_.Start();
 }
 
 void ChromotingHostContext::Stop() {