DevTools: DOM.setOuterHTML should work for detached documents

This patch fixes two bugs with DOM.setOuterHTML protocol method:
1. The method didn't work when a document node was passed as an argument
2. The method didn't work when document's element was removed

BUG=724974
R=pfeldman

Change-Id: I4f5dd0d9151fd80328af422e9016f63a749b0cf3
Reviewed-on: https://chromium-review.googlesource.com/745325Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512750}

third_party/WebKit/LayoutTests/inspector-protocol/dom/dom-setOuterHTML-detached-document-expected.txt

+Tests that setOuterHTML does not crash on detached document.
+{
+    id : <number>
+    result : {
+    }
+}
+

third_party/WebKit/LayoutTests/inspector-protocol/dom/dom-setOuterHTML-detached-document.js

+(async function(testRunner) {
+  var {page, session, dp} = await testRunner.startHTML(`
+    <div id="id">something</div> `, 'Tests that setOuterHTML does not crash on detached document.');
+
+  var message = await dp.DOM.getDocument();
+
+  await dp.Runtime.enable();
+  await dp.Runtime.evaluate({
+    expression: "document.documentElement.remove()"
+  });
+
+  var result = await dp.DOM.setOuterHTML({nodeId: message.result.root.nodeId, outerHTML: "<div>update</div>"});
+  testRunner.log(result);
+  testRunner.completeTest();
+})

third_party/WebKit/Source/core/inspector/DOMEditor.cpp

@@ -32,6 +32,7 @@
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/dom/DOMException.h"
+#include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/dom/Node.h"
 #include "core/dom/Text.h"
@@ -234,9 +235,12 @@ class DOMEditor::SetOuterHTMLAction final : public InspectorHistory::Action {
 
   bool Perform(ExceptionState& exception_state) override {
     old_html_ = CreateMarkup(node_.Get());
-    DCHECK(node_->ownerDocument());
-    DOMPatchSupport dom_patch_support(dom_editor_.Get(),
-                                      *node_->ownerDocument());
+    Document* document =
+        node_->IsDocumentNode() ? ToDocument(node_) : node_->ownerDocument();
+    DCHECK(document);
+    if (!document->documentElement())
+      return false;
+    DOMPatchSupport dom_patch_support(dom_editor_.Get(), *document);
     new_node_ =
         dom_patch_support.PatchNode(node_.Get(), html_, exception_state);
     return !exception_state.HadException();