Add partitionsOutOfMemoryUsingXXX to know Blink memory usage from OOM crash reports

Source/wtf/PartitionAlloc.h

Index: Source/wtf/PartitionAlloc.h
diff --git a/Source/wtf/PartitionAlloc.h b/Source/wtf/PartitionAlloc.h
index 1db9ab68245ce91cc9bd38dcd2886a8fc35b3603..f37e146e58f5843e09981a3291a31e952d8c6b89 100644
--- a/Source/wtf/PartitionAlloc.h
+++ b/Source/wtf/PartitionAlloc.h
@@ -316,6 +316,10 @@ struct WTF_EXPORT PartitionRootBase {
     // that.
     static PartitionPage gSeedPage;
     static PartitionBucket gPagedBucket;
+    // gMemoryUsageReportFunction is used to know how much memory Blink
+    // has already allocated when OOM occurrs.
+    // Currently Partitions registers this function.
+    static size_t (*gMemoryUsageReportFunction)();

[haraken, 2015/09/04 05:22:45]

Instead of exporting gMemoryUsageReportFunction, how about exporting
oomHandlingFunction? Then you can define oomHandlingFunction outside
PartitionAlloc and thus can do whatever you want. It would be more flexible.

[tasak, 2015/09/04 06:12:06]

Done.

 };
 
 // Never instantiate a PartitionRoot directly, instead use PartitionAlloc.
@@ -383,6 +387,7 @@ public:
     virtual void partitionsDumpBucketStats(const char* partitionName, const PartitionBucketMemoryStats*) = 0;
 };
 
+WTF_EXPORT void partitionAllocGlobalInit(size_t (*memoryUsageReportFunc)());
 WTF_EXPORT void partitionAllocInit(PartitionRoot*, size_t numBuckets, size_t maxAllocation);
 WTF_EXPORT bool partitionAllocShutdown(PartitionRoot*);
 WTF_EXPORT void partitionAllocGenericInit(PartitionRootGeneric*);