When sweeping is in progress, either finalize or do nothing

BUG=none
LOG=n
R=rmcilroy@chromium.org, hpayer@chromium.org

Review URL: https://codereview.chromium.org/1070653003

Cr-Commit-Position: refs/branch-heads/4.3@{#4}
Cr-Branched-From: f5c0a23-refs/heads/4.3.61@{#1}
Cr-Branched-From: 0a7d4f4-refs/heads/master@{#27508}

include/v8-version.h

@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 4
 #define V8_MINOR_VERSION 3
 #define V8_BUILD_NUMBER 61
-#define V8_PATCH_LEVEL 2
+#define V8_PATCH_LEVEL 3
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)

src/heap/gc-idle-time-handler.cc

@@ -253,9 +253,11 @@ GCIdleTimeAction GCIdleTimeHandler::Compute(double idle_time_in_ms,
   }
 
   // TODO(hpayer): Estimate finalize sweeping time.
-  if (heap_state.sweeping_in_progress &&
-      static_cast<size_t>(idle_time_in_ms) >= kMinTimeForFinalizeSweeping) {
-    return GCIdleTimeAction::FinalizeSweeping();
+  if (heap_state.sweeping_in_progress) {
+    if (static_cast<size_t>(idle_time_in_ms) >= kMinTimeForFinalizeSweeping) {
+      return GCIdleTimeAction::FinalizeSweeping();
+    }
+    return NothingOrDone();
   }
 
   if (heap_state.incremental_marking_stopped &&