Make it possible to have 1 PpapiGlobals per thread. Update unit tests.

ppapi/proxy/plugin_resource_tracker.h

Index: ppapi/proxy/plugin_resource_tracker.h
diff --git a/ppapi/proxy/plugin_resource_tracker.h b/ppapi/proxy/plugin_resource_tracker.h
index 35c2385ccf883f98a5c94e9711110b9c18d6cce2..8d098adab59224f8647bdbd50c4307dd528acc4b 100644
--- a/ppapi/proxy/plugin_resource_tracker.h
+++ b/ppapi/proxy/plugin_resource_tracker.h
@@ -9,7 +9,6 @@
 #include <utility>
 
 #include "base/compiler_specific.h"
-#include "base/synchronization/lock.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_stdint.h"
@@ -45,9 +44,6 @@ class PPAPI_PROXY_EXPORT PluginResourceTracker : public ResourceTracker {
   typedef std::map<HostResource, PP_Resource> HostResourceMap;
   HostResourceMap host_resource_map_;
 
-  // The global lock for the plugin side of the proxy.
-  base::Lock proxy_lock_;
-
   DISALLOW_COPY_AND_ASSIGN(PluginResourceTracker);
 };