blink: Enforce ParkableString thread restrictions when DCHECK_IS_ON().

Bug: 877044
Change-Id: I6b3e7be16ade21bd9c511a6a4fda10930575efa4
Reviewed-on: https://chromium-review.googlesource.com/1210782
Commit-Queue: Benoit L <lizeb@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589505}

third_party/blink/renderer/platform/bindings/parkable_string.cc

@@ -27,9 +27,19 @@ ParkableStringImpl::ParkableStringImpl(scoped_refptr<StringImpl>&& impl,
       lock_depth_(0),
       string_(std::move(impl)),
       is_parked_(false),
-      is_parkable_(parkable == ParkableState::kParkable) {}
+      is_parkable_(parkable == ParkableState::kParkable)
+#if DCHECK_IS_ON()
+      ,
+      owning_thread_(CurrentThread())
+#endif
+{
+}
 
 ParkableStringImpl::~ParkableStringImpl() {
+  // Null strings (default-constructed) can be destroyed on a different thread.
+  if (!string_.IsNull())
+    AssertOnValidThread();
+
   if (is_parkable_)
     ParkableStringManager::Instance().Remove(string_.Impl());
 }
@@ -46,24 +56,29 @@ void ParkableStringImpl::Unlock() {
 }
 
 bool ParkableStringImpl::Is8Bit() const {
+  AssertOnValidThread();
   return string_.Is8Bit();
 }
 
 bool ParkableStringImpl::IsNull() const {
+  AssertOnValidThread();
   return string_.IsNull();
 }
 
 const String& ParkableStringImpl::ToString() {
+  AssertOnValidThread();
   MutexLocker locker(mutex_);
   Unpark();
   return string_;
 }
 
 unsigned ParkableStringImpl::CharactersSizeInBytes() const {
+  AssertOnValidThread();
   return string_.CharactersSizeInBytes();
 }
 
 bool ParkableStringImpl::Park() {
+  AssertOnValidThread();
   MutexLocker locker(mutex_);
   DCHECK(is_parkable_);
 
@@ -79,6 +94,7 @@ bool ParkableStringImpl::Park() {
 }
 
 void ParkableStringImpl::Unpark() {
+  AssertOnValidThread();
   mutex_.AssertAcquired();
   if (!is_parked_)
     return;

third_party/blink/renderer/platform/bindings/parkable_string.h

@@ -15,6 +15,7 @@
 #include "third_party/blink/renderer/platform/platform_export.h"
 #include "third_party/blink/renderer/platform/wtf/ref_counted.h"
 #include "third_party/blink/renderer/platform/wtf/text/wtf_string.h"
+#include "third_party/blink/renderer/platform/wtf/threading.h"
 #include "third_party/blink/renderer/platform/wtf/threading_primitives.h"
 
 // ParkableString represents a string that may be parked in memory, that it its
@@ -87,6 +88,16 @@ class PLATFORM_EXPORT ParkableStringImpl final
 
   const bool is_parkable_;
 
+#if DCHECK_IS_ON()
+  const ThreadIdentifier owning_thread_;
+#endif
+
+  void AssertOnValidThread() const {
+#if DCHECK_IS_ON()
+    DCHECK_EQ(owning_thread_, CurrentThread());
+#endif
+  }
+
   FRIEND_TEST_ALL_PREFIXES(ParkableStringTest, Park);
   FRIEND_TEST_ALL_PREFIXES(ParkableStringTest, Unpark);
   FRIEND_TEST_ALL_PREFIXES(ParkableStringTest, LockUnlock);