Add support for `width` based Width Client Hint

Source/core/html/HTMLImageElementTest.cpp

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/html/HTMLImageElement.h"
+
+#include "core/dom/Document.h"
+#include "core/frame/FrameView.h"
+#include "core/testing/DummyPageHolder.h"
+#include <gtest/gtest.h>
+
+namespace blink {
+
+class HTMLImageElementTest : public testing::Test {
+protected:
+    HTMLImageElementTest()
+        : m_dummyPageHolder(DummyPageHolder::create(IntSize(500, 600)))
+    {
+    }
+
+    OwnPtr<DummyPageHolder> m_dummyPageHolder;
+};
+
+TEST_F(HTMLImageElementTest, width)
+{
+    RefPtrWillBeRawPtr<HTMLImageElement> image = HTMLImageElement::create(m_dummyPageHolder->document(), nullptr, /* createdByParser */ false);
+    image->setAttribute(HTMLNames::widthAttr, "400");
+    EXPECT_EQ(400, image->resourceWidth().width);
+    image->setAttribute(HTMLNames::sizesAttr, "100vw");
+    EXPECT_EQ(500, image->resourceWidth().width);

[Mike West, 2015/06/18 14:44:49]

Maybe make this a const along with the page's width?

+}
+
+TEST_F(HTMLImageElementTest, sourceSize)
+{
+    RefPtrWillBeRawPtr<HTMLImageElement> image = HTMLImageElement::create(m_dummyPageHolder->document(), nullptr, /* createdByParser */ false);
+    image->setAttribute(HTMLNames::widthAttr, "400");
+    EXPECT_EQ(500, image->sourceSize(*image));
+    image->setAttribute(HTMLNames::sizesAttr, "50vw");
+    EXPECT_EQ(250, image->sourceSize(*image));
+}
+
+} // namespace blink