[heap] Do more incremental marking work in tasks.

test/cctest/heap/test-spaces.cc

Index: test/cctest/heap/test-spaces.cc
diff --git a/test/cctest/heap/test-spaces.cc b/test/cctest/heap/test-spaces.cc
index 8eecc47b53e6a365e621541c7d8f535adadba1a8..7bc5a0643b6c3ff2c6363c2b7f7286676e6a3f60 100644
--- a/test/cctest/heap/test-spaces.cc
+++ b/test/cctest/heap/test-spaces.cc
@@ -449,6 +449,9 @@ TEST(CompactionSpace) {
 
 
 TEST(LargeObjectSpace) {
+  // This test does not initialize allocated objects, which confuses the
+  // incremental marker.
+  FLAG_incremental_marking = false;
   v8::V8::Initialize();
 
   LargeObjectSpace* lo = CcTest::heap()->lo_space();