Revert "Remove Deprecated ScopedBstr to BSTR Implicit Conversion Operator"

This reverts commit afb89420.

Reason for revert: seems this bortke the wind builder

https://ci.chromium.org/p/chromium/builders/ci/Win%20Builder/87976

Original change's description:
> Remove Deprecated ScopedBstr to BSTR Implicit Conversion Operator
> 
> BUG=1034666
> 
> Change-Id: I678af5925603de6f983e3d12da6832c0661f293c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042194
> Auto-Submit: Robert Liao <robliao@chromium.org>
> Commit-Queue: Will Harris <wfh@chromium.org>
> Reviewed-by: Will Harris <wfh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#739275}

TBR=robliao@chromium.org,wfh@chromium.org

Change-Id: Ica82a0dc2dadfc92792939cdef384285c4a4c989
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1034666
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2041979Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739280}

base/win/scoped_bstr.h

@@ -80,6 +80,9 @@ class BASE_EXPORT ScopedBstr {
   // Returns the number of bytes allocated for the BSTR.
   size_t ByteLength() const;
 
+  // DEPRECATED: Use ScopedBstr::Get() instead.
+  operator BSTR() const { return bstr_; }
+
   // Forbid comparison of ScopedBstr types.  You should never have the same
   // BSTR owned by two different scoped_ptrs.
   bool operator==(const ScopedBstr& bstr2) const = delete;