Reland of Avoid nuking everything when injecting stylesheet.

third_party/WebKit/Source/core/dom/StyleEngineTest.cpp

 // Copyright 2016 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 "core/dom/StyleEngine.h"
 
 #include "core/css/StyleSheetContents.h"
 #include "core/dom/Document.h"
+#include "core/dom/NodeComputedStyle.h"
 #include "core/frame/FrameView.h"
+#include "core/html/HTMLElement.h"
 #include "core/testing/DummyPageHolder.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
 
 class StyleEngineTest : public ::testing::Test {
 protected:
     void SetUp() override;
 
     Document& document() { return m_dummyPageHolder->document(); }
@@ skipping 13 matching lines @@
 TEST_F(StyleEngineTest, DocumentDirtyAfterInject)
 {
     RefPtrWillBeRawPtr<StyleSheetContents> parsedSheet = StyleSheetContents::create(CSSParserContext(document(), nullptr));
     parsedSheet->parseString("div {}");
     styleEngine().injectAuthorSheet(parsedSheet);
     document().view()->updateAllLifecyclePhases();
 
     EXPECT_TRUE(isDocumentStyleSheetCollectionClean());
 }
 
+TEST_F(StyleEngineTest, AnalyzedInject)
+{
+    document().body()->setInnerHTML("<style>div { color: red }</style><div id='t1'>Green</div><div></div>", ASSERT_NO_EXCEPTION);
+    document().view()->updateAllLifecyclePhases();
+
+    Element* t1 = document().getElementById("t1");
+    ASSERT_TRUE(t1);
+    ASSERT_TRUE(t1->computedStyle());
+    EXPECT_EQ(makeRGB(255, 0, 0), t1->computedStyle()->visitedDependentColor(CSSPropertyColor));
+
+    unsigned beforeCount = styleEngine().styleForElementCount();
+
+    RefPtrWillBeRawPtr<StyleSheetContents> parsedSheet = StyleSheetContents::create(CSSParserContext(document(), nullptr));
+    parsedSheet->parseString("#t1 { color: green }");
+    styleEngine().injectAuthorSheet(parsedSheet);
+    document().view()->updateAllLifecyclePhases();
+
+    unsigned afterCount = styleEngine().styleForElementCount();
+    EXPECT_EQ(1u, afterCount - beforeCount);
+
+    ASSERT_TRUE(t1->computedStyle());
+    EXPECT_EQ(makeRGB(0, 128, 0), t1->computedStyle()->visitedDependentColor(CSSPropertyColor));
+}
+
 } // namespace blink