Fix null pointer exception in WebViewColorOverlay.

Discovered this while debugging WorkerTest.SharedWorkerHttpAuth for
Bug 106383.

BUG=103386
TEST=None


Review URL: http://codereview.chromium.org/8771055

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113417 0039d316-1c4b-4281-b951-d872f2087c98

chrome/renderer/webview_color_overlay.cc

@@ -25,7 +25,8 @@ WebViewColorOverlay::WebViewColorOverlay(content::RenderView* render_view,
 }
 
 WebViewColorOverlay::~WebViewColorOverlay() {
-  render_view_->GetWebView()->removePageOverlay(this);
+  if (render_view_->GetWebView())
+    render_view_->GetWebView()->removePageOverlay(this);
 }
 
 void WebViewColorOverlay::paintPageOverlay(WebKit::WebCanvas* canvas) {