[tracing] Support BACKGROUND mode in MemoryCache dump provider

third_party/WebKit/Source/platform/SharedBuffer.cpp

Index: third_party/WebKit/Source/platform/SharedBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/SharedBuffer.cpp b/third_party/WebKit/Source/platform/SharedBuffer.cpp
index 6bfbe81f3e8940552b034a05be04357f242a4c2c..6220ed7d4f29b3672647658844fe8ac3548915e2 100644
--- a/third_party/WebKit/Source/platform/SharedBuffer.cpp
+++ b/third_party/WebKit/Source/platform/SharedBuffer.cpp
@@ -275,12 +275,13 @@ void SharedBuffer::onMemoryDump(const String& dumpPrefix, WebProcessMemoryDump*
         WebMemoryAllocatorDump* dump = memoryDump->createMemoryAllocatorDump(dumpPrefix + "/shared_buffer");
         dump->addScalar("size", "bytes", m_buffer.size());
         memoryDump->addSuballocation(dump->guid(), String(WTF::Partitions::kAllocatedObjectPoolName));
-    } else {
+    }
+    if (m_segments.size()) {
         // If there is data in the segments, then it should have been allocated
         // using fastMalloc.
         const String dataDumpName = dumpPrefix + "/segments";
         auto dump = memoryDump->createMemoryAllocatorDump(dataDumpName);
-        dump->addScalar("size", "bytes", m_size);
+        dump->addScalar("size", "bytes", m_size - m_buffer.size());
         memoryDump->addSuballocation(dump->guid(), String(WTF::Partitions::kAllocatedObjectPoolName));
     }
 }