[heap] replace DisableInlineAllocationSteps with PauseAllocationObservers

* DisableInlineAllocationSteps was a blunt hammer added to work around
  tests that needed to avoid artificially lower limits imposed by
  observers. PauseAllocationObserversScope can properly disable step on
  a temporary basis.
* Modify tests. Remove DisableInlineAllocationSteps.

This exposed a bug in allocation observers: we were not doing a step
when a fresh page is added.

Fix this by moving the step into UpdateAllocationInfo. We should be
doing a step (and keeping top_on_previous_step_ consistent) whenever
we move move top(). UpdateAllocationInfo is the correct place for this
rather than the callers of UpdateAllocationInfo.

Bug: 
Change-Id: I2edc238dc2e73bf9a2e9738c2a9b50efcac5cbf0
Reviewed-on: https://chromium-review.googlesource.com/821052
Commit-Queue: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50052}

src/heap/spaces.cc

@@ -2056,8 +2056,11 @@ LocalAllocationBuffer& LocalAllocationBuffer::operator=(
 
 
 void NewSpace::UpdateAllocationInfo() {
+  Address new_top = to_space_.page_low();
+  InlineAllocationStep(top(), new_top, nullptr, 0);
+
   MemoryChunk::UpdateHighWaterMark(allocation_info_.top());
-  allocation_info_.Reset(to_space_.page_low(), to_space_.page_high());
+  allocation_info_.Reset(new_top, to_space_.page_high());
   original_top_.SetValue(top());
   original_limit_.SetValue(limit());
   UpdateInlineAllocationLimit(0);
@@ -2066,7 +2069,6 @@ void NewSpace::UpdateAllocationInfo() {
 
 
 void NewSpace::ResetAllocationInfo() {
-  Address old_top = allocation_info_.top();
   to_space_.Reset();
   UpdateAllocationInfo();
   // Clear all mark-bits in the to-space.
@@ -2077,7 +2079,6 @@ void NewSpace::ResetAllocationInfo() {
     // Concurrent marking may have local live bytes for this page.
     heap()->concurrent_marking()->ClearLiveness(p);
   }
-  InlineAllocationStep(old_top, allocation_info_.top(), nullptr, 0);
 }
 
 
@@ -2138,8 +2139,6 @@ bool NewSpace::EnsureAllocation(int size_in_bytes,
       return false;
     }
 
-    InlineAllocationStep(old_top, allocation_info_.top(), nullptr, 0);
-
     old_top = allocation_info_.top();
     high = to_space_.page_high();
     filler_size = Heap::GetFillToAlign(old_top, alignment);

src/heap/spaces.h

@@ -2681,11 +2681,6 @@ class NewSpace : public SpaceWithLinearArea {
   // it in steps to guarantee that the observers are notified periodically.
   void UpdateInlineAllocationLimit(int size_in_bytes);
 
-  void DisableInlineAllocationSteps() {
-    top_on_previous_step_ = 0;
-    UpdateInlineAllocationLimit(0);
-  }
-
   // Get the extent of the inactive semispace (for use as a marking stack,
   // or to zap it). Notice: space-addresses are not necessarily on the
   // same page, so FromSpaceStart() might be above FromSpaceEnd().

test/cctest/heap/heap-utils.cc

@@ -72,7 +72,6 @@ std::vector<Handle<FixedArray>> CreatePadding(Heap* heap, int padding_size,
     int overall_free_memory = static_cast<int>(heap->old_space()->Available());
     CHECK(padding_size <= overall_free_memory || overall_free_memory == 0);
   } else {
-    heap->new_space()->DisableInlineAllocationSteps();
     int overall_free_memory =
         static_cast<int>(*heap->new_space()->allocation_limit_address() -
                          *heap->new_space()->allocation_top_address());
@@ -105,7 +104,7 @@ std::vector<Handle<FixedArray>> CreatePadding(Heap* heap, int padding_size,
 
 void AllocateAllButNBytes(v8::internal::NewSpace* space, int extra_bytes,
                           std::vector<Handle<FixedArray>>* out_handles) {
-  space->DisableInlineAllocationSteps();
+  PauseAllocationObserversScope pause_observers(space->heap());
   int space_remaining = static_cast<int>(*space->allocation_limit_address() -
                                          *space->allocation_top_address());
   CHECK(space_remaining >= extra_bytes);
@@ -124,7 +123,7 @@ void FillCurrentPage(v8::internal::NewSpace* space,
 
 bool FillUpOnePage(v8::internal::NewSpace* space,
                    std::vector<Handle<FixedArray>>* out_handles) {
-  space->DisableInlineAllocationSteps();
+  PauseAllocationObserversScope pause_observers(space->heap());
   int space_remaining = static_cast<int>(*space->allocation_limit_address() -
                                          *space->allocation_top_address());
   if (space_remaining == 0) return false;