Add operator<< to StyleDifference for debug logging.

third_party/WebKit/Source/core/style/StyleDifferenceTest.cpp

Index: third_party/WebKit/Source/core/style/StyleDifferenceTest.cpp
diff --git a/third_party/WebKit/Source/core/style/StyleDifferenceTest.cpp b/third_party/WebKit/Source/core/style/StyleDifferenceTest.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..51c09624288f028e6f5e17fb322709e5c8e4f730
--- /dev/null
+++ b/third_party/WebKit/Source/core/style/StyleDifferenceTest.cpp
@@ -0,0 +1,60 @@
+// Copyright 2017 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/style/StyleDifference.h"
+
+#include <sstream>
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blink {
+
+TEST(StyleDifferenceTest, StreamOutputDefault) {
+  std::stringstream stringStream;
+  StyleDifference diff;
+  stringStream << diff;
+  EXPECT_EQ(
+      "StyleDifference{layoutType=NoLayout, "
+      "paintInvalidationType=NoPaintInvalidation, recomputeOverflow=0, "
+      "propertySpecificDifferences=, scrollAnchorDisablingPropertyChanged=0}",
+      stringStream.str());
+}
+
+TEST(StyleDifferenceTest, StreamOutputAllFieldsMutated) {
+  std::stringstream stringStream;
+  StyleDifference diff;
+  diff.setNeedsPaintInvalidationObject();
+  diff.setNeedsPositionedMovementLayout();
+  diff.setNeedsRecomputeOverflow();
+  diff.setTransformChanged();
+  diff.setScrollAnchorDisablingPropertyChanged();
+  stringStream << diff;
+  EXPECT_EQ(
+      "StyleDifference{layoutType=PositionedMovement, "
+      "paintInvalidationType=PaintInvalidationObject, recomputeOverflow=1, "
+      "propertySpecificDifferences=TransformChanged, "
+      "scrollAnchorDisablingPropertyChanged=1}",
+      stringStream.str());
+}
+
+TEST(StyleDifferenceTest, StreamOutputSetAllProperties) {
+  std::stringstream stringStream;
+  StyleDifference diff;
+  diff.setTransformChanged();
+  diff.setOpacityChanged();
+  diff.setZIndexChanged();
+  diff.setFilterChanged();
+  diff.setBackdropFilterChanged();
+  diff.setCSSClipChanged();
+  diff.setTextDecorationOrColorChanged();
+  stringStream << diff;
+  EXPECT_EQ(
+      "StyleDifference{layoutType=NoLayout, "
+      "paintInvalidationType=NoPaintInvalidation, recomputeOverflow=0, "
+      "propertySpecificDifferences=TransformChanged|OpacityChanged|"
+      "ZIndexChanged|FilterChanged|BackdropFilterChanged|CSSClipChanged|"
+      "TextDecorationOrColorChanged, scrollAnchorDisablingPropertyChanged=0}",
+      stringStream.str());
+}
+
+}  // namespace blink