[headless] Fix headless_shell compilation.

- DevTools removed wasThrown from results, use GetExceptionDetails
  instead.

R=skyostil@chromium.org

BUG=546953

Review-Url: https://codereview.chromium.org/2246113004
Cr-Commit-Position: refs/heads/master@{#412205}

headless/app/headless_shell.cc

@@ -209,7 +209,7 @@ class HeadlessShell : public HeadlessWebContents::Observer,
   }
 
   void OnDomFetched(std::unique_ptr<runtime::EvaluateResult> result) {
-    if (result->GetWasThrown()) {
+    if (result->GetExceptionDetails()) {
       LOG(ERROR) << "Failed to evaluate document.body.innerHTML";
     } else {
       std::string dom;