[Linux] Do not try to call readdir() on a null DIR* in base::ProcessIterator.

base/process/process_iterator_linux.cc

Index: base/process/process_iterator_linux.cc
diff --git a/base/process/process_iterator_linux.cc b/base/process/process_iterator_linux.cc
index a9d044c53824f7cd74f1a1c9717a51f0fefc5dfb..e2d0123e3ca13fa6a98ee949de6d8486fdea6109 100644
--- a/base/process/process_iterator_linux.cc
+++ b/base/process/process_iterator_linux.cc
@@ -59,18 +59,26 @@ bool GetProcCmdline(pid_t pid, std::vector<std::string>* proc_cmd_line_args) {
 ProcessIterator::ProcessIterator(const ProcessFilter* filter)
     : filter_(filter) {
   procfs_dir_ = opendir(internal::kProcDir);
+  if (!procfs_dir_) {

[Nico, 2016/01/27 18:54:34]

Can you add a comment when this can happen? From the bug, sounds like this can
happen on Android -- and it kind of sounds like it might happen there
consistently. Is it useful to LOG(ERROR) about this on android when this happens
if it's going to happen every time there?

What do we use ProcessIterator for on Android? I thought it's mostly for task
manager and about:memory etc, which don't exist there.

[Robert Sesek, 2016/01/27 18:58:42]

Added a comment. This *shouldn't* happen every time, it seems like the SELinux
policies may not be sorted out right.
Given what nnk@ wrote on the bug, it seems like collecting memory stats this way
isn't going to work anyways. I'll file a bug with the person who wrote
memory_details_android.cc.

[Robert Sesek, 2016/01/27 19:11:11]

Filed https://code.google.com/p/chromium/issues/detail?id=581778

+    PLOG(ERROR) << "opendir " << internal::kProcDir;
+  }
 }
 
 ProcessIterator::~ProcessIterator() {
   if (procfs_dir_) {
     closedir(procfs_dir_);
-    procfs_dir_ = NULL;
+    procfs_dir_ = nullptr;
   }
 }
 
 bool ProcessIterator::CheckForNextProcess() {
   // TODO(port): skip processes owned by different UID
 
+  if (!procfs_dir_) {
+    DLOG(ERROR) << "Skipping CheckForNextProcess(), no procfs_dir_";
+    return false;
+  }
+
   pid_t pid = kNullProcessId;
   std::vector<std::string> cmd_line_args;
   std::string stats_data;