Revert of [DevTools] Move 'this' evaluation from ExecutionContext to autocomplete.

third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.js

Index: third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.js b/third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.js
index 85a4834693db0d93d77fe9f843133b15c7192d7e..4edc2a27233dcc7c3ba6d8f3f5f5cf75e64db21e 100644
--- a/third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.js
+++ b/third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.js
@@ -544,6 +544,11 @@
       generatePreview,
       userGesture,
       callback) {
+    if (!expression) {
+      // There is no expression, so the completion should happen against global properties.
+      expression = 'this';
+    }
+
     /**
      * @this {SDK.ExecutionContext}
      * @param {?Protocol.Error} error