Make the v8 Isolate used in the proxy resolver explicit.

net/proxy/proxy_resolver_v8.h

Index: net/proxy/proxy_resolver_v8.h
diff --git a/net/proxy/proxy_resolver_v8.h b/net/proxy/proxy_resolver_v8.h
index 823e93a08cde9c70c70e02df077f34c624a1cac9..326b5a4ad2cdf6b76a3cabe63273912e28637d99 100644
--- a/net/proxy/proxy_resolver_v8.h
+++ b/net/proxy/proxy_resolver_v8.h
@@ -10,6 +10,10 @@
 #include "net/base/net_export.h"
 #include "net/proxy/proxy_resolver.h"
 
+namespace v8 {
+class Isolate;
+}  // namespace v8
+
 namespace net {
 
 // Implementation of ProxyResolver that uses V8 to evaluate PAC scripts.
@@ -85,7 +89,14 @@ class NET_EXPORT_PRIVATE ProxyResolverV8 : public ProxyResolver {
       const scoped_refptr<ProxyResolverScriptData>& script_data,
       const net::CompletionCallback& /*callback*/) OVERRIDE;
 
+  // Remember the default Isolate, must be called from the main thread. This
+  // hack can be removed when the "default Isolate" concept is gone.
+  static void RememberDefaultIsolate();
+  static v8::Isolate* GetDefaultIsolate();
+
  private:
+  static v8::Isolate* g_default_isolate_;
+
   // Context holds the Javascript state for the most recently loaded PAC
   // script. It corresponds with the data from the last call to
   // SetPacScript().