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

content/child/child_discardable_shared_memory_manager.cc

Index: content/child/child_discardable_shared_memory_manager.cc
diff --git a/content/child/child_discardable_shared_memory_manager.cc b/content/child/child_discardable_shared_memory_manager.cc
index cbe069a27cb011318629a84669ef22ec83331aa7..011f2d43cd35f17b13befd3d8c6889e41a1c1c44 100644
--- a/content/child/child_discardable_shared_memory_manager.cc
+++ b/content/child/child_discardable_shared_memory_manager.cc
@@ -31,10 +31,10 @@ class DiscardableMemoryImpl : public base::DiscardableMemory {
  public:
   DiscardableMemoryImpl(ChildDiscardableSharedMemoryManager* manager,
                         scoped_ptr<DiscardableSharedMemoryHeap::Span> span)
-      : manager_(manager), span_(span.Pass()), is_locked_(true) {}
+      : manager_(manager), span_(span.Pass()) {}
 
   ~DiscardableMemoryImpl() override {
-    if (is_locked_)
+    if (span_->is_locked())
       manager_->UnlockSpan(span_.get());
 
     manager_->ReleaseSpan(span_.Pass());
@@ -42,22 +42,20 @@ class DiscardableMemoryImpl : public base::DiscardableMemory {
 
   // Overridden from base::DiscardableMemory:
   bool Lock() override {
-    DCHECK(!is_locked_);
+    DCHECK(!span_->is_locked());
 
     if (!manager_->LockSpan(span_.get()))
       return false;
 
-    is_locked_ = true;
     return true;
   }
   void Unlock() override {
-    DCHECK(is_locked_);
+    DCHECK(span_->is_locked());
 
     manager_->UnlockSpan(span_.get());
-    is_locked_ = false;
   }
   void* data() const override {
-    DCHECK(is_locked_);
+    DCHECK(span_->is_locked());
     return reinterpret_cast<void*>(span_->start() * base::GetPageSize());
   }
 
@@ -70,7 +68,6 @@ class DiscardableMemoryImpl : public base::DiscardableMemory {
  private:
   ChildDiscardableSharedMemoryManager* const manager_;
   scoped_ptr<DiscardableSharedMemoryHeap::Span> span_;
-  bool is_locked_;
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryImpl);
 };
@@ -137,12 +134,9 @@ ChildDiscardableSharedMemoryManager::AllocateLockedDiscardableMemory(
 
     // Attempt to lock |free_span|. Delete span and search free lists again
     // if locking failed.
-    if (free_span->shared_memory()->Lock(
-            free_span->start() * base::GetPageSize() -
-                reinterpret_cast<size_t>(free_span->shared_memory()->memory()),
-            free_span->length() * base::GetPageSize()) ==
+    if (free_span->Lock(base::GetPageSize()) ==
         base::DiscardableSharedMemory::FAILED) {
-      DCHECK(!free_span->shared_memory()->IsMemoryResident());
+      DCHECK(!free_span->IsMemoryResident());
       // We have to release purged memory before |free_span| can be destroyed.
       heap_.ReleasePurgedMemory();
       DCHECK(!free_span->shared_memory());
@@ -184,10 +178,7 @@ ChildDiscardableSharedMemoryManager::AllocateLockedDiscardableMemory(
   if (pages < pages_to_allocate) {
     scoped_ptr<DiscardableSharedMemoryHeap::Span> leftover =
         heap_.Split(new_span.get(), pages);
-    leftover->shared_memory()->Unlock(
-        leftover->start() * base::GetPageSize() -
-            reinterpret_cast<size_t>(leftover->shared_memory()->memory()),
-        leftover->length() * base::GetPageSize());
+    leftover->Unlock(base::GetPageSize());
     heap_.MergeIntoFreeLists(leftover.Pass());
   }
 
@@ -223,15 +214,11 @@ bool ChildDiscardableSharedMemoryManager::LockSpan(
   if (!span->shared_memory())
     return false;
 
-  size_t offset = span->start() * base::GetPageSize() -
-      reinterpret_cast<size_t>(span->shared_memory()->memory());
-  size_t length = span->length() * base::GetPageSize();
-
-  switch (span->shared_memory()->Lock(offset, length)) {
+  switch (span->Lock(base::GetPageSize())) {
     case base::DiscardableSharedMemory::SUCCESS:
       return true;
     case base::DiscardableSharedMemory::PURGED:
-      span->shared_memory()->Unlock(offset, length);
+      span->Unlock(base::GetPageSize());
       return false;
     case base::DiscardableSharedMemory::FAILED:
       return false;
@@ -246,11 +233,8 @@ void ChildDiscardableSharedMemoryManager::UnlockSpan(
   base::AutoLock lock(lock_);
 
   DCHECK(span->shared_memory());
-  size_t offset = span->start() * base::GetPageSize() -
-      reinterpret_cast<size_t>(span->shared_memory()->memory());
-  size_t length = span->length() * base::GetPageSize();
 
-  return span->shared_memory()->Unlock(offset, length);
+  return span->Unlock(base::GetPageSize());
 }
 
 void ChildDiscardableSharedMemoryManager::ReleaseSpan(