Fix pre-order traversal in LayoutBoxModelObject::HasNonEmptyLayoutSize

Passing 'this' (which |object| will be in this case) to
LayoutObject::NextInPreOrder, will turn it into a non-obvious way of
saying FirstChild.
Pass |root| instead of |object| to make the traversal actually pre-
order.

Bug: 769459
Change-Id: I6bc4c487faab053d02bc16826862234f15e2376e
Reviewed-on: https://chromium-review.googlesource.com/690254Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#505099}

third_party/WebKit/Source/core/exported/WebElementTest.cpp

@@ -65,6 +65,12 @@ static const char kBlockWithEmptyInlines[] =
     "  <span></span> "
     "</div>";
 
+static const char kBlockWithEmptyFirstChild[] =
+    "<div id='testElement'>"
+    "  <div style='position: absolute'></div> "
+    "  <div style='position: absolute'>Hello</div> "
+    "</div>";
+
 class WebElementTest : public ::testing::Test {
  protected:
   Document& GetDocument() { return page_holder_->GetDocument(); }
@@ -124,6 +130,9 @@ TEST_F(WebElementTest, HasNonEmptyLayoutSize) {
       GetDocument().getElementById("testElement")->CreateShadowRootInternal();
   root.SetInnerHTMLFromString("<div>Hello World</div>");
   EXPECT_TRUE(TestElement().HasNonEmptyLayoutSize());
+
+  InsertHTML(kBlockWithEmptyFirstChild);
+  EXPECT_TRUE(TestElement().HasNonEmptyLayoutSize());
 }
 
 TEST_F(WebElementTest, IsEditable) {

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

@@ -593,7 +593,7 @@ bool LayoutBoxModelObject::HasNonEmptyLayoutSize() const {
   for (const LayoutBoxModelObject* root = this; root;
        root = root->Continuation()) {
     for (const LayoutObject* object = root; object;
-         object = object->NextInPreOrder(object)) {
+         object = object->NextInPreOrder(root)) {
       if (object->IsBox()) {
         const LayoutBox& box = ToLayoutBox(*object);
         if (box.LogicalHeight() && box.LogicalWidth())