Fix encoding of the string returned from Node::ToString().

https://chromium-review.googlesource.com/c/chromium/src/+/920776 caused
regressions. Strings dumped from LayoutObject::DumpLayoutObject() used
to escape newlines, non-ASCII characters and other special characters,
but not after this CL. The code depended on a special std::ostream&
operator<<(std::ostream& out, const String& string) overload, which took
care of this string conversion. Since we no longer use std::ostream,
introduce add String::EncodeForDebugging() and have Node::ToString()
(and the aforementioned operator<< overload) use that.

Added a unit test so that we don't accidentally break this again.

Change-Id: I62172bf1ebd12da1fdb71f78768e17aa937ea5cb
Reviewed-on: https://chromium-review.googlesource.com/925271Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537719}

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

@@ -1700,9 +1700,8 @@ static void DumpAttributeDesc(const Node& node,
     return;
   builder.Append(' ');
   builder.Append(name.ToString());
-  builder.Append("=\"");
-  builder.Append(value);
-  builder.Append("\"");
+  builder.Append("=");
+  builder.Append(String(value).EncodeForDebugging());
 }
 
 std::ostream& operator<<(std::ostream& ostream, const Node& node) {
@@ -1732,9 +1731,8 @@ String Node::ToString() const {
   StringBuilder builder;
   builder.Append(nodeName());
   if (IsTextNode()) {
-    builder.Append(" \"");
-    builder.Append(nodeValue());
-    builder.Append("\"");
+    builder.Append(" ");
+    builder.Append(nodeValue().EncodeForDebugging());
     return builder.ToString();
   }
   DumpAttributeDesc(*this, HTMLNames::idAttr, builder);

third_party/WebKit/Source/core/layout/LayoutObjectTest.cpp

@@ -675,4 +675,34 @@ TEST_F(LayoutObjectTest, DisplayContentsWrapperInTableCell) {
   EXPECT_EQ(cell->GetLayoutObject(), none->GetLayoutObject()->Parent());
 }
 
+TEST_F(LayoutObjectTest, DumpLayoutObject) {
+  // Test dumping for debugging, in particular that newlines and non-ASCII
+  // characters are escaped as expected.
+  SetBodyInnerHTML(String::FromUTF8(R"HTML(
+    <div id='block' style='background:
+lime'>
+      testing Среќен роденден
+</div>
+  )HTML"));
+
+  LayoutObject* block = GetLayoutObjectByElementId("block");
+  ASSERT_TRUE(block);
+  LayoutObject* text = block->SlowFirstChild();
+  ASSERT_TRUE(text);
+
+  StringBuilder result;
+  block->DumpLayoutObject(result, false, 0);
+  EXPECT_EQ(
+      result.ToString(),
+      String("LayoutBlockFlow\tDIV id=\"block\" style=\"background:\\nlime\""));
+
+  result.Clear();
+  text->DumpLayoutObject(result, false, 0);
+  EXPECT_EQ(
+      result.ToString(),
+      String("LayoutText\t#text \"\\n      testing "
+             "\\u0421\\u0440\\u0435\\u045C\\u0435\\u043D "
+             "\\u0440\\u043E\\u0434\\u0435\\u043D\\u0434\\u0435\\u043D\\n\""));
+}
+
 }  // namespace blink

third_party/WebKit/Source/platform/wtf/text/WTFString.cpp

@@ -374,6 +374,52 @@ String String::Format(const char* format, ...) {
   return String(reinterpret_cast<const LChar*>(buffer.data()), length);
 }
 
+String String::EncodeForDebugging() const {
+  if (IsNull())
+    return "<null>";
+
+  String str;
+  str.append('"');
+  for (unsigned index = 0; index < length(); ++index) {
+    // Print shorthands for select cases.
+    UChar character = (*impl_)[index];
+    switch (character) {
+      case '\t':
+        str.append("\\t");
+        break;
+      case '\n':
+        str.append("\\n");
+        break;
+      case '\r':
+        str.append("\\r");
+        break;
+      case '"':
+        str.append("\\\"");
+        break;
+      case '\\':
+        str.append("\\\\");
+        break;
+      default:
+        if (IsASCIIPrintable(character)) {
+          str.append(static_cast<char>(character));
+        } else {
+          // Print "\uXXXX" for control or non-ASCII characters.
+          str.append("\\u");
+          std::stringstream out;
+          out.width(4);
+          out.fill('0');
+          out.setf(std::ios_base::hex, std::ios_base::basefield);
+          out.setf(std::ios::uppercase);
+          out << character;
+          str.append(out.str().c_str());
+        }
+        break;
+    }
+  }
+  str.append('"');
+  return str;
+}
+
 template <typename IntegerType>
 static String IntegerToString(IntegerType input) {
   IntegerToStringConverter<IntegerType> converter(input);
@@ -774,45 +820,7 @@ String String::FromUTF8WithLatin1Fallback(const LChar* string, size_t size) {
 }
 
 std::ostream& operator<<(std::ostream& out, const String& string) {
-  if (string.IsNull())
-    return out << "<null>";
-
-  out << '"';
-  for (unsigned index = 0; index < string.length(); ++index) {
-    // Print shorthands for select cases.
-    UChar character = string[index];
-    switch (character) {
-      case '\t':
-        out << "\\t";
-        break;
-      case '\n':
-        out << "\\n";
-        break;
-      case '\r':
-        out << "\\r";
-        break;
-      case '"':
-        out << "\\\"";
-        break;
-      case '\\':
-        out << "\\\\";
-        break;
-      default:
-        if (IsASCIIPrintable(character)) {
-          out << static_cast<char>(character);
-        } else {
-          // Print "\uXXXX" for control or non-ASCII characters.
-          out << "\\u";
-          out.width(4);
-          out.fill('0');
-          out.setf(std::ios_base::hex, std::ios_base::basefield);
-          out.setf(std::ios::uppercase);
-          out << character;
-        }
-        break;
-    }
-  }
-  return out << '"';
+  return out << string.EncodeForDebugging().Utf8().data();
 }
 
 #ifndef NDEBUG

third_party/WebKit/Source/platform/wtf/text/WTFString.h

@@ -335,6 +335,10 @@ class WTF_EXPORT String {
   // This function supports Latin-1 characters only.
   PRINTF_FORMAT(1, 2) static String Format(const char* format, ...);
 
+  // Returns a version suitable for gtest and base/logging.*.  It prepends and
+  // appends double-quotes, and escapes chracters other than ASCII printables.
+  String EncodeForDebugging() const;
+
   // Returns an uninitialized string. The characters needs to be written
   // into the buffer returned in data before the returned string is used.
   // Failure to do this will have unpredictable results.