Revert of [heap] Take page lock when scavenging old to new references in...

Revert of [heap] Take page lock when scavenging old to new references in Scavenger. (patchset #2 id:20001 of https://codereview.chromium.org/2781363002/ )

Reason for revert:
This results in a deadlock when the scavenger decides to perform sweeping and re-grabs the same mutex.

Original issue's description:
> [heap] Take page lock when scavenging old to new references in Scavenger.
>
> BUG=v8:5807
>
> Review-Url: https://codereview.chromium.org/2781363002
> Cr-Commit-Position: refs/heads/master@{#44268}
> Committed: https://chromium.googlesource.com/v8/v8/+/4024e6a1bb0b803a5cd16fcd11f39cc305b943c6

TBR=ulan@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5807

Review-Url: https://codereview.chromium.org/2786313003
Cr-Commit-Position: refs/heads/master@{#44302}

src/heap/heap.cc

@@ -1723,14 +1723,12 @@ void Heap::Scavenge() {
   {
     // Copy objects reachable from the old generation.
     TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_OLD_TO_NEW_POINTERS);
-    RememberedSet<OLD_TO_NEW>::Iterate(
-        this, SYNCHRONIZED, [this](Address addr) {
-          return Scavenger::CheckAndScavengeObject(this, addr);
-        });
+    RememberedSet<OLD_TO_NEW>::Iterate(this, [this](Address addr) {
+      return Scavenger::CheckAndScavengeObject(this, addr);
+    });
 
     RememberedSet<OLD_TO_NEW>::IterateTyped(
-        this, SYNCHRONIZED,
-        [this](SlotType type, Address host_addr, Address addr) {
+        this, [this](SlotType type, Address host_addr, Address addr) {
           return UpdateTypedSlotHelper::UpdateTypedSlot(
               isolate(), type, addr, [this](Object** addr) {
                 // We expect that objects referenced by code are long living.

src/heap/mark-compact.cc

@@ -2369,12 +2369,11 @@ void MinorMarkCompactCollector::MarkLiveObjects() {
   {
     TRACE_GC(heap()->tracer(),
              GCTracer::Scope::MINOR_MC_MARK_OLD_TO_NEW_POINTERS);
-    RememberedSet<OLD_TO_NEW>::Iterate(
-        heap(), NON_SYNCHRONIZED,
-        [this](Address addr) { return CheckAndMarkObject(heap(), addr); });
+    RememberedSet<OLD_TO_NEW>::Iterate(heap(), [this](Address addr) {
+      return CheckAndMarkObject(heap(), addr);
+    });
     RememberedSet<OLD_TO_NEW>::IterateTyped(
-        heap(), NON_SYNCHRONIZED,
-        [this](SlotType type, Address host_addr, Address addr) {
+        heap(), [this](SlotType type, Address host_addr, Address addr) {
           return UpdateTypedSlotHelper::UpdateTypedSlot(
               isolate(), type, addr, [this](Object** addr) {
                 return CheckAndMarkObject(heap(),

src/heap/remembered-set.h

@@ -13,8 +13,6 @@
 namespace v8 {
 namespace internal {
 
-enum RememberedSetIterationMode { SYNCHRONIZED, NON_SYNCHRONIZED };
-
 // TODO(ulan): Investigate performance of de-templatizing this class.
 template <RememberedSetType type>
 class RememberedSet : public AllStatic {
@@ -100,13 +98,9 @@ class RememberedSet : public AllStatic {
   // Iterates and filters the remembered set with the given callback.
   // The callback should take (Address slot) and return SlotCallbackResult.
   template <typename Callback>
-  static void Iterate(Heap* heap, RememberedSetIterationMode mode,
-                      Callback callback) {
-    IterateMemoryChunks(heap, [mode, callback](MemoryChunk* chunk) {
-      if (mode == SYNCHRONIZED) chunk->mutex()->Lock();
-      Iterate(chunk, callback);
-      if (mode == SYNCHRONIZED) chunk->mutex()->Unlock();
-    });
+  static void Iterate(Heap* heap, Callback callback) {
+    IterateMemoryChunks(
+        heap, [callback](MemoryChunk* chunk) { Iterate(chunk, callback); });
   }
 
   // Iterates over all memory chunks that contains non-empty slot sets.
@@ -183,12 +177,9 @@ class RememberedSet : public AllStatic {
   // The callback should take (SlotType slot_type, SlotAddress slot) and return
   // SlotCallbackResult.
   template <typename Callback>
-  static void IterateTyped(Heap* heap, RememberedSetIterationMode mode,
-                           Callback callback) {
-    IterateMemoryChunks(heap, [mode, callback](MemoryChunk* chunk) {
-      if (mode == SYNCHRONIZED) chunk->mutex()->Lock();
+  static void IterateTyped(Heap* heap, Callback callback) {
+    IterateMemoryChunks(heap, [callback](MemoryChunk* chunk) {
       IterateTyped(chunk, callback);
-      if (mode == SYNCHRONIZED) chunk->mutex()->Unlock();
     });
   }