[tracing] Display the locked size of discardable memory segment.

content/common/discardable_shared_memory_heap.h

Index: content/common/discardable_shared_memory_heap.h
diff --git a/content/common/discardable_shared_memory_heap.h b/content/common/discardable_shared_memory_heap.h
index 100b03f169611388e16d601276913d119cca3f64..ce8787a6f7396a61ea29af9247f41aa41e325749 100644
--- a/content/common/discardable_shared_memory_heap.h
+++ b/content/common/discardable_shared_memory_heap.h
@@ -30,6 +30,7 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
     base::DiscardableSharedMemory* shared_memory() { return shared_memory_; }
     size_t start() const { return start_; }
     size_t length() const { return length_; }
+    void set_is_locked(bool is_locked) { is_locked_ = is_locked; }
 
    private:
     friend class DiscardableSharedMemoryHeap;
@@ -41,6 +42,7 @@ class CONTENT_EXPORT DiscardableSharedMemoryHeap {
     base::DiscardableSharedMemory* shared_memory_;
     size_t start_;
     size_t length_;
+    bool is_locked_;
 
     DISALLOW_COPY_AND_ASSIGN(Span);
   };