[GC] Change behavior when reaching external allocation limit

With the recent changes to the incremental marking API we can now kick off
incremental marking while respecting callback flags.

Performance neutral for smoothness.image_decoding_cases on N9 (read: does not
crash) as long as we synchronously process phantom callbacks
(kGCCallbackFlagForced).

OORT single run:
  "marksweep": {
    "count": 5,
    "pause_min": 7.5,
    "pause_max": 158.8,
    "pause_avg": 97.52000000000001,
    "pause_gt_10ms": 4
  }
  --- vs ---
  "marksweep": {
    "count": 5,
    "pause_min": 16.2,
    "pause_max": 22.1,
    "pause_avg": 19.32,
    "pause_gt_10ms": 5
  }

The number of actual full GCs varies. The improvement manifests in reduced
maximum and average pauses.

BUG=chromium:515795
LOG=N

Review URL: https://codereview.chromium.org/1271253002

Cr-Commit-Position: refs/heads/master@{#30028}

src/api.cc

@@ -6884,8 +6884,20 @@ Local<Integer> v8::Integer::NewFromUnsigned(Isolate* isolate, uint32_t value) {
 
 
 void Isolate::CollectAllGarbage(const char* gc_reason) {
-  reinterpret_cast<i::Isolate*>(this)->heap()->CollectAllGarbage(
-      i::Heap::kNoGCFlags, gc_reason, v8::kGCCallbackFlagForced);
+  i::Heap* heap = reinterpret_cast<i::Isolate*>(this)->heap();
+  if (heap->incremental_marking()->IsStopped()) {
+    heap->StartIncrementalMarking(i::Heap::kNoGCFlags, kGCCallbackFlagForced,
+                                  gc_reason);
+  }
+  // TODO(mlippautz): Compute the time slice for incremental marking based on
+  // memory pressure.
+  double deadline = heap->MonotonicallyIncreasingTimeInMs() +
+                    i::FLAG_external_allocation_limit_incremental_time;
+  heap->AdvanceIncrementalMarking(0, deadline,
+                                  i::IncrementalMarking::StepActions(
+                                      i::IncrementalMarking::GC_VIA_STACK_GUARD,
+                                      i::IncrementalMarking::FORCE_MARKING,
+                                      i::IncrementalMarking::FORCE_COMPLETION));
 }
 
 

src/flag-definitions.h

@@ -810,6 +810,10 @@ DEFINE_BOOL(manual_evacuation_candidates_selection, false,
             "Test mode only flag. It allows an unit test to select evacuation "
             "candidates pages (requires --stress_compaction).")
 
+// api.cc
+DEFINE_INT(external_allocation_limit_incremental_time, 1,
+           "Time spent in incremental marking steps (in ms) once the external "
+           "allocation limit is reached")
 
 //
 // Dev shell flags