[tracing] Fix light dump of partition alloc dump provider

Partition Alloc dump provider dumps bucket stats for the case of
DirectMap objects even for ligth dumps. This CL fixes this issue.

BUG=613198

Review-Url: https://codereview.chromium.org/2045643002
Cr-Commit-Position: refs/heads/master@{#398206}

third_party/WebKit/Source/wtf/allocator/PartitionAlloc.cpp

@@ -1360,17 +1360,20 @@ void partitionDumpStatsGeneric(PartitionRootGeneric* partition, const char* part
 
     size_t directMappedAllocationsTotalSize = 0;
     for (size_t i = 0; i < numDirectMappedAllocations; ++i) {
+        uint32_t size = directMapLengths[i];
+        directMappedAllocationsTotalSize += size;
+        if (isLightDump)
+            continue;
+
         PartitionBucketMemoryStats stats;
         memset(&stats, '\0', sizeof(stats));
         stats.isValid = true;
         stats.isDirectMap = true;
         stats.numFullPages = 1;
-        uint32_t size = directMapLengths[i];
         stats.allocatedPageSize = size;
         stats.bucketSlotSize = size;
         stats.activeBytes = size;
         stats.residentBytes = size;
-        directMappedAllocationsTotalSize += size;
         partitionStatsDumper->partitionsDumpBucketStats(partitionName, &stats);
     }
     partitionStats.totalResidentBytes += directMappedAllocationsTotalSize;