Add crash keys about field trial shared memory errors.

base/memory/shared_memory.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MEMORY_SHARED_MEMORY_H_
 #define BASE_MEMORY_SHARED_MEMORY_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 45 matching lines @@
   // When opening an existing object, this has no effect.
   size_t size = 0;
 
   // If true, mappings might need to be made executable later.
   bool executable = false;
 
   // If true, the file can be shared read-only to a process.
   bool share_read_only = false;
 };
 
+// Enumeration of different shared memory error types. Note: Currently only
+// errors from Mac POSIX shared memory implementation are fully instrumented.
+// TODO(asvitkine): Evaluate whether we want to keep this ability after
+// crbug.com/703649 is fixed and expand to all platforms or remove.
+enum class SharedMemoryError {
+  NO_ERRORS,
+  NO_FILE,
+  BAD_PARAMS,
+  STAT_FAILED,
+  TRUNCATE_FAILED,
+  NO_TEMP_DIR,
+  MAKE_READONLY_FAILED,
+  INODE_MISMATCH,
+  MMAP_FAILED,
+};
+
 // Platform abstraction for shared memory.
 // SharedMemory consumes a SharedMemoryHandle [potentially one that it created]
 // to map a shared memory OS resource into the virtual address space of the
 // current process.
 class BASE_EXPORT SharedMemory {
  public:
   SharedMemory();
 
 #if defined(OS_WIN)
   // Similar to the default constructor, except that this allows for
@@ skipping 149 matching lines @@
     size_t operator()(const UniqueId& id) const {
       return HashInts(id.first, id.second);
     }
   };
 
   // Returns a unique ID for this shared memory's handle. Note this function may
   // access file system and be slow.
   bool GetUniqueId(UniqueId* id) const;
 #endif
 
+  // Returns the last error encountered as a result of a call to Create() or
+  // Map(). Note: Currently only errors from Mac POSIX shared memory
+  // implementation are fully instrumented.
+  // TODO(asvitkine): Evaluate whether we want to keep this ability after
+  // crbug.com/703649 is fixed and expand to all platforms or remove.
+  SharedMemoryError get_last_error() const { return last_error_; }
+
  private:
 #if defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_ANDROID) && \
     (!defined(OS_MACOSX) || defined(OS_IOS))
   bool FilePathForMemoryName(const std::string& mem_name, FilePath* path);
 #endif
 
 #if defined(OS_WIN)
   // If true indicates this came from an external source so needs extra checks
   // before being mapped.
   bool external_section_;
@@ skipping 11 matching lines @@
   SharedMemoryHandle::Type mapped_memory_mechanism_;
 #endif
 
   // The OS primitive that backs the shared memory region.
   SharedMemoryHandle shm_;
 
   size_t             mapped_size_;
   void*              memory_;
   bool               read_only_;
   size_t             requested_size_;
+  SharedMemoryError last_error_ = SharedMemoryError::NO_ERRORS;

[Nico, 2017/05/10 15:12:22]

nit: please init in ctor, like for all other members of this class

[Alexei Svitkine (slow), 2017/05/10 15:22:39]

Unfortunately, it's not a single ctor - it's 7 different ones spread between
_mac.cc, _win.cc and _posix.cc. Seems like a lot of churn to add it to all of
them, especially if it ends up being temporary. So my preference would be to
keep as-is unless you have a really strong objection.

 
   DISALLOW_COPY_AND_ASSIGN(SharedMemory);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_H_