PartitionAlloc: API changes to support new partitionPurgeMemoryGeneric() mode.

Source/wtf/Partitions.cpp

Index: Source/wtf/Partitions.cpp
diff --git a/Source/wtf/Partitions.cpp b/Source/wtf/Partitions.cpp
index c8f6e7500d803eea15b326e87bbd67075f7f1111..e1c9510dd565d0feb00d29a0876620701f7c3fb4 100644
--- a/Source/wtf/Partitions.cpp
+++ b/Source/wtf/Partitions.cpp
@@ -76,10 +76,10 @@ void Partitions::decommitFreeableMemory()
 {
     ASSERT(isMainThread());
 
-    partitionPurgeMemoryGeneric(bufferPartition());
-    partitionPurgeMemoryGeneric(fastMallocPartition());
-    partitionPurgeMemory(objectModelPartition());
-    partitionPurgeMemory(layoutPartition());
+    partitionPurgeMemoryGeneric(bufferPartition(), PartitionPurgeDecommitEmptyPages);
+    partitionPurgeMemoryGeneric(fastMallocPartition(), PartitionPurgeDecommitEmptyPages);
+    partitionPurgeMemory(objectModelPartition(), PartitionPurgeDecommitEmptyPages);
+    partitionPurgeMemory(layoutPartition(), PartitionPurgeDecommitEmptyPages);
 }
 
 void Partitions::reportMemoryUsageHistogram()