win: Capture some CRITICAL_SECTION debugging data

snapshot/win/process_snapshot_win.h

Index: snapshot/win/process_snapshot_win.h
diff --git a/snapshot/win/process_snapshot_win.h b/snapshot/win/process_snapshot_win.h
index a38ac5e9382b2cf16e9ba5295df2c2534d7f6e08..c9edfac3e94d598963a4a1fff4dc260b249833be 100644
--- a/snapshot/win/process_snapshot_win.h
+++ b/snapshot/win/process_snapshot_win.h
@@ -59,12 +59,18 @@ class ProcessSnapshotWin final : public ProcessSnapshot {
   //! \param[in] process The handle to create a snapshot from.
   //! \param[in] suspension_state Whether \a process has been suspended by the
   //!     caller.
+  //! \param[in] debug_critical_section_address The address in the target
+  //!     process's address space of a `CRITICAL_SECTION` allocated with valid
+  //!     `.DebugInfo`. Used as a starting point to walk the process's locks.
+  //!     May be `0`.
   //!
   //! \return `true` if the snapshot could be created, `false` otherwise with
   //!     an appropriate message logged.
   //!
   //! \sa ScopedProcessSuspend
-  bool Initialize(HANDLE process, ProcessSuspensionState suspension_state);
+  bool Initialize(HANDLE process,
+                  ProcessSuspensionState suspension_state,
+                  WinVMAddress debug_critical_section_address);
 
   //! \brief Initializes the object's exception.
   //!
@@ -138,9 +144,10 @@ class ProcessSnapshotWin final : public ProcessSnapshot {
   // Initializes modules_ on behalf of Initialize().
   void InitializeModules();
 
-  // Initializes peb_memory_ on behalf of Initialize().
+  // Initializes various memory blocks reachable from the PEB on behalf of
+  // Initialize().
   template <class Traits>
-  void InitializePebData();
+  void InitializePebData(WinVMAddress debug_critical_section_address);
 
   void AddMemorySnapshot(WinVMAddress address,
                          WinVMSize size,
@@ -160,8 +167,16 @@ class ProcessSnapshotWin final : public ProcessSnapshot {
   WinVMSize DetermineSizeOfEnvironmentBlock(
       WinVMAddress start_of_environment_block);
 
+  // Starting from the address of a CRITICAL_SECTION, walks the doubly-linked
+  // list stored in RTL_CRITICAL_SECTION.DebugInfo.ProcessLocksList adding both
+  // the RTL_CRITICAL_SECTION and the RTL_CRITICAL_SECTION_DEBUG memory blocks
+  // to the snapshot.
+  template <class Traits>
+  void ReadLocks(WinVMAddress start,
+                 PointerVector<internal::MemorySnapshotWin>* into);
+
   internal::SystemSnapshotWin system_;
-  PointerVector<internal::MemorySnapshotWin> peb_memory_;
+  PointerVector<internal::MemorySnapshotWin> extra_memory_;
   PointerVector<internal::ThreadSnapshotWin> threads_;
   PointerVector<internal::ModuleSnapshotWin> modules_;
   scoped_ptr<internal::ExceptionSnapshotWin> exception_;