Add crash keys about field trial shared memory errors.

base/memory/shared_memory.h

Index: base/memory/shared_memory.h
diff --git a/base/memory/shared_memory.h b/base/memory/shared_memory.h
index 35067e6aaeab848080c681fa729f7853df720f3c..52303d800d83bead006cd3d18e81388eb928959f 100644
--- a/base/memory/shared_memory.h
+++ b/base/memory/shared_memory.h
@@ -63,6 +63,22 @@ struct BASE_EXPORT SharedMemoryCreateOptions {
   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
@@ -232,6 +248,13 @@ class BASE_EXPORT SharedMemory {
   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))
@@ -263,6 +286,7 @@ class BASE_EXPORT SharedMemory {
   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);
 };