Don't create a v8 isolate in ppapi tests

The unit test framework brings up blink, so we have an initialized
isolate we can just use.

BUG=none
R=andrewhayden@chromium.org,dmichael@chromium.org

Review URL: https://codereview.chromium.org/537543002

Cr-Commit-Position: refs/heads/master@{#293133}

content/renderer/pepper/npapi_glue.cc

@@ -189,15 +189,10 @@ PP_Var NPObjectToPPVar(PepperPluginInstanceImpl* instance, NPObject* object) {
 
 PP_Var NPObjectToPPVarForTest(PepperPluginInstanceImpl* instance,
                               NPObject* object) {
-  v8::Isolate* test_isolate = v8::Isolate::New();
   PP_Var result = PP_MakeUndefined();
-  {
-    v8::HandleScope scope(test_isolate);
-    v8::Isolate::Scope isolate_scope(test_isolate);
-    v8::Local<v8::Context> context = v8::Context::New(test_isolate);
+  v8::HandleScope scope(instance->GetIsolate());
+  v8::Local<v8::Context> context = v8::Context::New(instance->GetIsolate());
   result = NPObjectToPPVarImpl(instance, object, context);
-  }
-  test_isolate->Dispose();
   return result;
 }