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..946eef0ee572068af9ddc95ff33485bda5a34830 100644
--- a/third_party/WebKit/Source/wtf/text/StringImpl.cpp
+++ b/third_party/WebKit/Source/wtf/text/StringImpl.cpp
@@ -32,6 +32,7 @@
 #include "wtf/allocator/Partitions.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/AtomicStringTable.h"
+#include "wtf/text/CString.h"
 #include "wtf/text/CharacterNames.h"
 #include "wtf/text/StringBuffer.h"
 #include "wtf/text/StringHash.h"
@@ -54,8 +55,10 @@ 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 +327,13 @@ bool StringImpl::isSafeToSendToAnotherThread() const {
   return false;
 }
 
+#if DCHECK_IS_ON()
+std::string StringImpl::asciiForDebugging() const {
+  CString ascii = String(this->isolatedCopy()).left(128).ascii();

[esprehn, 2017/01/12 23:00:00]

just use substring, that's all left() does anyway:

String(substring(0, 128)).ascii()

no need to copy.

[Charlie Harrison, 2017/01/13 17:42:25]

substring is not const because it can ref |this| (afaict). We need const
correctness here. I think the isolated copy isn't a big deal because we only do
this when we crash.

+  return std::string(ascii.data(), ascii.length());
+}
+#endif
+
 PassRefPtr<StringImpl> StringImpl::createUninitialized(unsigned length,
                                                        LChar*& data) {
   if (!length) {