Increment style version for all style changes.

Source/core/dom/DocumentTest.cpp

 /*
  * Copyright (c) 2014, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 306 matching lines @@
     EXPECT_EQ("https://www.example.com/hoge", document().outgoingReferrer());
 }
 
 TEST_F(DocumentTest, OutgoingReferrerWithUniqueOrigin)
 {
     document().setURL(KURL(KURL(), "https://www.example.com/hoge#fuga?piyo"));
     document().setSecurityOrigin(SecurityOrigin::createUnique());
     EXPECT_EQ(String(), document().outgoingReferrer());
 }
 
+TEST_F(DocumentTest, StyleVersion)
+{
+    setHtmlInnerHTML(
+        "<style>"
+        "    .a * { color: green }"
+        "    .b .c { color: green }"
+        "</style>"
+        "<div id='x'><span class='c'></span></div>");
+
+    Element* element = document().getElementById("x");
+    EXPECT_TRUE(element);
+
+    uint64_t previousStyleVersion = document().styleVersion();
+    element->setAttribute(blink::HTMLNames::classAttr, "notfound");
+    EXPECT_EQ(previousStyleVersion, document().styleVersion());
+
+    document().view()->updateAllLifecyclePhases();
+
+    previousStyleVersion = document().styleVersion();
+    element->setAttribute(blink::HTMLNames::classAttr, "a");
+    EXPECT_NE(previousStyleVersion, document().styleVersion());
+
+    document().view()->updateAllLifecyclePhases();
+
+    previousStyleVersion = document().styleVersion();
+    element->setAttribute(blink::HTMLNames::classAttr, "a b");
+    EXPECT_NE(previousStyleVersion, document().styleVersion());
+}
+
 } // namespace blink