DevTools: [hosted mode] avoid exception in devtools_compatibility:addExtensions

third_party/WebKit/Source/devtools/front_end/devtools_compatibility.js

Index: third_party/WebKit/Source/devtools/front_end/devtools_compatibility.js
diff --git a/third_party/WebKit/Source/devtools/front_end/devtools_compatibility.js b/third_party/WebKit/Source/devtools/front_end/devtools_compatibility.js
index ab5ebefc94005178f36eb7e5c186e187dd3e7992..c9b517b534dac533c71ac83a3ac1a8e67162df92 100644
--- a/third_party/WebKit/Source/devtools/front_end/devtools_compatibility.js
+++ b/third_party/WebKit/Source/devtools/front_end/devtools_compatibility.js
@@ -64,10 +64,14 @@
      */
     addExtensions(extensions) {
       // Support for legacy front-ends (<M41).
-      if (window['WebInspector'] && window['WebInspector']['addExtensions'])
+      if (window['WebInspector'] && window['WebInspector']['addExtensions']) {
         window['WebInspector']['addExtensions'](extensions);
-      else
+      } else if (window['InspectorFrontendAPI']) {
+        // The addExtensions command is sent as the onload event happens for
+        // DevTools front-end. In case of hosted mode, this
+        // happens before the InspectorFrontendAPI is initialized.
         this._dispatchOnInspectorFrontendAPI('addExtensions', [extensions]);
+      }
     }
 
     /**