DevTools: set extension name as human-readable name of isolated world

The patch sets up human-readable name of isolated worlds, generated by
extension, to the name of the parent extension. This will be very useful
for extension debugging in developer tools.

BUG=160977
R=vsevik, yurys

Review URL: https://codereview.chromium.org/500823002

Cr-Commit-Position: refs/heads/master@{#293095}

extensions/renderer/script_injection.cc

@@ -84,6 +84,9 @@ int GetIsolatedWorldIdForExtension(const Extension* extension,
   frame->setIsolatedWorldContentSecurityPolicy(
       id,
       blink::WebString::fromUTF8(CSPInfo::GetContentSecurityPolicy(extension)));
+  frame->setIsolatedWorldHumanReadableName(
+      id,
+      blink::WebString::fromUTF8(extension->name()));
 
   return id;
 }