Oilpan: Implement a GC to take a heap snapshot

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index b3f0aa7aef5d34aff5c7c8f16fcf1377c92ee7d5..70a2ca016ea320e778995f7431f196d1e368d668 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -853,6 +853,13 @@ void ThreadState::makeConsistentForGC()
         m_heaps[i]->makeConsistentForGC();
 }
 
+void ThreadState::makeConsistentForMutator()
+{
+    ASSERT(isInGC());
+    for (int i = 0; i < NumberOfHeaps; ++i)
+        m_heaps[i]->makeConsistentForMutator();
+}
+
 void ThreadState::preGC()
 {
     ASSERT(!isInGC());
@@ -885,9 +892,23 @@ void ThreadState::postGC(GCType gcType)
     }
 #endif
 
-    setGCState(gcType == GCWithSweep ? EagerSweepScheduled : LazySweepScheduled);
     for (int i = 0; i < NumberOfHeaps; i++)
         m_heaps[i]->prepareForSweep();
+
+    if (gcType == GCWithSweep) {
+        setGCState(EagerSweepScheduled);
+    } else if (gcType == GCWithoutSweep) {
+        setGCState(LazySweepScheduled);
+    } else {
+        takeSnapshot();
+
+        // This unmarks all marked objects and marks all unmarked objects dead.
+        makeConsistentForMutator();
+
+        // Force setting NoGCScheduled to circumvent checkThread()
+        // in setGCState().
+        m_gcState = NoGCScheduled;
+    }
 }
 
 void ThreadState::preSweep()
@@ -1297,6 +1318,12 @@ void ThreadState::promptlyFreed(size_t gcInfoIndex)
     m_likelyToBePromptlyFreed[entryIndex] += 3;
 }
 
+void ThreadState::takeSnapshot()
+{
+    ASSERT(isInGC());
+    // TODO(ssid): Implement this.
+}
+
 #if ENABLE(GC_PROFILING)
 const GCInfo* ThreadState::findGCInfoFromAllThreads(Address address)
 {