Make RenderView not have to know about how PhishingClassifierDelegate.

chrome/renderer/safe_browsing/phishing_thumbnailer.cc

Index: chrome/renderer/safe_browsing/phishing_thumbnailer.cc
===================================================================
--- chrome/renderer/safe_browsing/phishing_thumbnailer.cc	(revision 73993)
+++ chrome/renderer/safe_browsing/phishing_thumbnailer.cc	(working copy)
@@ -28,8 +28,7 @@
                                const gfx::Size& view_size,
                                const gfx::Size& thumbnail_size) {
   if (!render_view || !render_view->webview()) {
-    NOTREACHED();
-    return SkBitmap();
+    return SkBitmap();  // The WebView is going away.
   }
   WebView* view = render_view->webview();
   base::TimeTicks beginning_time = base::TimeTicks::Now();