Don't try to set the empty string as the preferred set.

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

Index: third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
diff --git a/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp b/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
index da6ca9d5d107a85ed355a43256baf4db658dd210..d6979b2c8da494b263afc2928dbcbfbce2a69cec 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
+++ b/third_party/WebKit/Source/core/dom/StyleEngineTest.cpp
@@ -557,4 +557,21 @@ TEST_F(StyleEngineTest, NoScheduledRuleSetInvalidationsOnNewShadow) {
   EXPECT_FALSE(GetDocument().NeedsStyleInvalidation());
 }
 
+TEST_F(StyleEngineTest, EmptyHttpEquivDefaultStyle) {
+  GetDocument().body()->setInnerHTML(
+      "<style>div { color:pink }</style><div id=container></div>");
+  GetDocument().View()->UpdateAllLifecyclePhases();
+
+  EXPECT_FALSE(GetStyleEngine().NeedsActiveStyleUpdate());
+
+  Element* container = GetDocument().getElementById("container");
+  ASSERT_TRUE(container);
+  container->setInnerHTML("<meta http-equiv='default-style' content=''>");
+  EXPECT_FALSE(GetStyleEngine().NeedsActiveStyleUpdate());
+
+  container->setInnerHTML(
+      "<meta http-equiv='default-style' content='preferred'>");
+  EXPECT_TRUE(GetStyleEngine().NeedsActiveStyleUpdate());
+}
+
 }  // namespace blink