Fix race in HostSharedBitmapManager::AllocatedBitmapCount

This race should be benign, because the count is just used for a heuristic and can't truly be synchronized anyway, but best to use a lock with the access.

BUG=417194

Review URL: https://codereview.chromium.org/604583002

Cr-Commit-Position: refs/heads/master@{#296554}

content/common/host_shared_bitmap_manager.cc

@@ -187,6 +187,11 @@ void HostSharedBitmapManager::ProcessRemoved(
   process_map_.erase(proc_it);
 }
 
+size_t HostSharedBitmapManager::AllocatedBitmapCount() const {
+  base::AutoLock lock(lock_);
+  return handle_map_.size();
+}
+
 void HostSharedBitmapManager::FreeSharedMemoryFromMap(
     cc::SharedBitmap* bitmap) {
   base::AutoLock lock(lock_);

content/common/host_shared_bitmap_manager.h

@@ -65,12 +65,12 @@ class CONTENT_EXPORT HostSharedBitmapManager : public cc::SharedBitmapManager {
   void ChildDeletedSharedBitmap(const cc::SharedBitmapId& id);
   void ProcessRemoved(base::ProcessHandle process_handle);
 
-  size_t AllocatedBitmapCount() const { return handle_map_.size(); }
+  size_t AllocatedBitmapCount() const;
 
  private:
   void FreeSharedMemoryFromMap(cc::SharedBitmap* bitmap);
 
-  base::Lock lock_;
+  mutable base::Lock lock_;
 
   typedef base::hash_map<cc::SharedBitmapId, scoped_refptr<BitmapData> >
       BitmapMap;