Bug 1536697 - Fix error handling in base::SharedMemory::Map. r=froydnj

If mmap failed, we'd leave the memory_ member variable set to MAP_FAILED,
but everything else in this file checks for nullptr (and only nullptr) to
test if the pointer is valid.

Also, this removes the debug assertion that the mmap succeeded, to allow
writing unit tests where we expect it to fail (e.g., for insufficient
permissions).

Depends on D26747

Differential Revision: https://phabricator.services.mozilla.com/D26748

--HG--
extra : moz-landing-system : lando

ipc/chromium/src/base/shared_memory_posix.cc

@@ -290,29 +290,28 @@ bool SharedMemory::Freeze() {
 
 bool SharedMemory::Map(size_t bytes, void* fixed_address) {
   if (mapped_file_ == -1) return false;
+  DCHECK(!memory_);
 
   // Don't use MAP_FIXED when a fixed_address was specified, since that can
   // replace pages that are alread mapped at that address.
-  memory_ =
+  void* mem =
       mmap(fixed_address, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
            MAP_SHARED, mapped_file_, 0);
 
-  bool mmap_succeeded = memory_ != MAP_FAILED;
-
-  DCHECK(mmap_succeeded) << "Call to mmap failed, errno=" << errno;
-
-  if (mmap_succeeded) {
-    if (fixed_address && memory_ != fixed_address) {
-      bool munmap_succeeded = munmap(memory_, bytes) == 0;
-      DCHECK(munmap_succeeded) << "Call to munmap failed, errno=" << errno;
-      memory_ = NULL;
-      return false;
-    }
-
-    mapped_size_ = bytes;
+  if (mem == MAP_FAILED) {
+    CHROMIUM_LOG(WARNING) << "Call to mmap failed: " << strerror(errno);
+    return false;
   }
 
-  return mmap_succeeded;
+  if (fixed_address && mem != fixed_address) {
+    bool munmap_succeeded = munmap(mem, bytes) == 0;
+    DCHECK(munmap_succeeded) << "Call to munmap failed, errno=" << errno;
+    return false;
+  }
+
+  memory_ = mem;
+  mapped_size_ = bytes;
+  return true;
 }
 
 bool SharedMemory::Unmap() {