Add operator<< to StyleDifference for debug logging.

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

Index: third_party/WebKit/Source/core/style/StyleDifference.cpp
diff --git a/third_party/WebKit/Source/core/style/StyleDifference.cpp b/third_party/WebKit/Source/core/style/StyleDifference.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..cd085be9ad8e42bde4008f4c8d5b1a2beb20d8ca
--- /dev/null
+++ b/third_party/WebKit/Source/core/style/StyleDifference.cpp
@@ -0,0 +1,87 @@
+// 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"
+
+namespace blink {
+
+std::ostream& operator<<(std::ostream& out, const StyleDifference& diff) {
+  out << "StyleDifference{layoutType=";
+
+  switch (diff.m_layoutType) {
+    case StyleDifference::NoLayout:
+      out << "NoLayout";
+      break;
+    case StyleDifference::PositionedMovement:
+      out << "PositionedMovement";
+      break;
+    case StyleDifference::FullLayout:
+      out << "FullLayout";
+      break;
+    default:
+      NOTREACHED();
+      break;
+  }
+
+  out << ", paintInvalidationType=";
+  switch (diff.m_paintInvalidationType) {
+    case StyleDifference::NoPaintInvalidation:
+      out << "NoPaintInvalidation";
+      break;
+    case StyleDifference::PaintInvalidationObject:
+      out << "PaintInvalidationObject";
+      break;
+    case StyleDifference::PaintInvalidationSubtree:
+      out << "PaintInvalidationSubtree";
+      break;
+    default:
+      NOTREACHED();
+      break;
+  }
+
+  out << ", recomputeOverflow=" << diff.m_recomputeOverflow;
+
+  out << ", propertySpecificDifferences=";
+  int diffCount = 0;
+  for (int i = 0; i < StyleDifference::kPropertyDifferenceCount; i++) {
+    unsigned bitTest = 1 << i;
+    if (diff.m_propertySpecificDifferences & bitTest) {
+      if (diffCount++ > 0)
+        out << "|";
+      switch (bitTest) {
+        case StyleDifference::TransformChanged:
+          out << "TransformChanged";
+          break;
+        case StyleDifference::OpacityChanged:
+          out << "OpacityChanged";
+          break;
+        case StyleDifference::ZIndexChanged:
+          out << "ZIndexChanged";
+          break;
+        case StyleDifference::FilterChanged:
+          out << "FilterChanged";
+          break;
+        case StyleDifference::BackdropFilterChanged:
+          out << "BackdropFilterChanged";
+          break;
+        case StyleDifference::CSSClipChanged:
+          out << "CSSClipChanged";
+          break;
+        case StyleDifference::TextDecorationOrColorChanged:
+          out << "TextDecorationOrColorChanged";
+          break;
+        default:
+          NOTREACHED();
+          break;
+      }
+    }
+  }
+
+  out << ", scrollAnchorDisablingPropertyChanged="
+      << diff.m_scrollAnchorDisablingPropertyChanged;
+
+  return out << "}";
+}
+
+}  // namespace blink