Replace NULL with nullptr

Also fixed some lines that were too long, and a few other minor
details.

Change-Id: I6efba5fb6e03eb5d0a300fddb2a75bf8e2f175cb
diff --git a/imgdiag/imgdiag.cc b/imgdiag/imgdiag.cc
index 34a4c14..1056fe1 100644
--- a/imgdiag/imgdiag.cc
+++ b/imgdiag/imgdiag.cc
@@ -97,7 +97,8 @@
 
     {
       struct stat sts;
-      std::string proc_pid_str = StringPrintf("/proc/%ld", static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
+      std::string proc_pid_str =
+          StringPrintf("/proc/%ld", static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
       if (stat(proc_pid_str.c_str(), &sts) == -1) {
         os << "Process does not exist";
         return false;
@@ -144,7 +145,8 @@
     const size_t pointer_size = InstructionSetPointerSize(
         Runtime::Current()->GetInstructionSet());
 
-    std::string file_name = StringPrintf("/proc/%ld/mem", static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
+    std::string file_name =
+        StringPrintf("/proc/%ld/mem", static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
 
     size_t boot_map_size = boot_map.end - boot_map.start;
 
@@ -197,8 +199,8 @@
       return false;
     }
 
-    std::string page_map_file_name = StringPrintf("/proc/%ld/pagemap",
-                                                  static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
+    std::string page_map_file_name = StringPrintf(
+        "/proc/%ld/pagemap", static_cast<long>(image_diff_pid));  // NOLINT [runtime/int]
     auto page_map_file = std::unique_ptr<File>(OS::OpenFileForReading(page_map_file_name.c_str()));
     if (page_map_file == nullptr) {
       os << "Failed to open " << page_map_file_name << " for reading: " << strerror(errno);
@@ -226,8 +228,10 @@
       return false;
     }
 
-    std::set<size_t> dirty_page_set_remote;  // Set of the remote virtual page indices that are dirty
-    std::set<size_t> dirty_page_set_local;   // Set of the local virtual page indices that are dirty
+    // Set of the remote virtual page indices that are dirty
+    std::set<size_t> dirty_page_set_remote;
+    // Set of the local virtual page indices that are dirty
+    std::set<size_t> dirty_page_set_local;
 
     size_t different_int32s = 0;
     size_t different_bytes = 0;