Enable ThreadRestrictionVerifier for StringImpl

third_party/WebKit/Source/wtf/text/StringImpl.cpp

Index: third_party/WebKit/Source/wtf/text/StringImpl.cpp
diff --git a/third_party/WebKit/Source/wtf/text/StringImpl.cpp b/third_party/WebKit/Source/wtf/text/StringImpl.cpp
index 641fbc9c72c4b7aeecf2ff0d48498bb7d27e2e20..a74a1c57be92e27f52d8906cffa53bcc41e82f14 100644
--- a/third_party/WebKit/Source/wtf/text/StringImpl.cpp
+++ b/third_party/WebKit/Source/wtf/text/StringImpl.cpp
@@ -54,8 +54,10 @@ namespace WTF {
 
 using namespace Unicode;
 
+#if !DCHECK_IS_ON()
 static_assert(sizeof(StringImpl) == 3 * sizeof(int),
               "StringImpl should stay small");
+#endif
 
 #ifdef STRING_STATS
 
@@ -324,6 +326,18 @@ bool StringImpl::isSafeToSendToAnotherThread() const {
   return false;
 }
 
+#if DCHECK_IS_ON()
+std::string StringImpl::asciiForDebugging() const {
+  const unsigned kMaxCheckLength = 64;
+  std::string debugString;
+  for (unsigned i = 0; i < length() && i < kMaxCheckLength; ++i) {
+    UChar c = (*this)[i];
+    debugString.push_back(isASCIIPrintable(c) ? c : '?');
+  }
+  return debugString;

[esprehn, 2017/01/11 22:34:01]

This function can be:

CString ascii = left(64).ascii();
return std::string(ascii.data(), ascii.length());

[Charlie Harrison, 2017/01/12 16:42:30]

Ah right, for some reason I was concerned with pulling in CString here but I
forget why.

[Charlie Harrison, 2017/01/12 22:50:08]

Actually, left is a function of String, so it would have to be
String(this).left(..)...

Unfortunately unless we const_cast this we'll lose the const correctness of
hasOneRef(). I've changed it to use isolatedCopy().

+}
+#endif
+
 PassRefPtr<StringImpl> StringImpl::createUninitialized(unsigned length,
                                                        LChar*& data) {
   if (!length) {