Remove implicit conversions from scoped_refptr to T* in sync/

Committed: https://crrev.com/12c173d02d9306bdd180a4535d55aabf581b4c33
Cr-Commit-Position: refs/heads/master@{#291804}

[dcheng, 2014-08-25 21:11:25]

Unfortunately, we can't make scoped_refptr testable until the conversion
operator has been removed. While it would be possible to disable the conversion
operator and make it testable in the same patch, the automated tool tries to
skip rewriting code where manual cleanups would be useful. This includes things
like:

// What if ReturnsScopedRefPtr() creates a new object internally?
if (ReturnsScopedRefPtr())

Foo* Bar() {
  const scoped_refptr<Foo>& f = ReturnsScopedRefPtr();
  return f;  // Does the return type need to be rewritten? Or is .get() safe?
}

Doing this in one patch would make catching some of these instances (in
particular, a boolean test on a temporary scoped_refptr) more difficult. As a
result, the work is being split into several steps:
Step 1: Rewrite all implicit conversions to be explicit (or rewrite the receiver
type to scoped_refptr<T>, if the tool believes the conversion to be unsafe).
Step 2: Once a platform compiles cleanly without the conversion operator, #ifdef
the conversion operator out.
Step 3: Make scoped_refptr testable on that platform.
Step 4: Remove unnecessary calls to .get().

[rlarocque, 2014-08-25 22:22:43]

rlarocque@chromium.org changed reviewers:
+ zea@chromium.org

[rlarocque, 2014-08-25 22:22:43]

lgtm

[dcheng, 2014-08-25 22:26:11]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2014-08-25 22:28:01]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dcheng@chromium.org/503903002/1

[commit-bot: I haz the power, 2014-08-26 00:07:16]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-26 00:07:18]

Failed to commit the patch.

[dcheng, 2014-08-26 00:25:55]

Committed patchset #1 to pending queue manually as 8de071f (presubmit
successful).

[commit-bot: I haz the power, 2014-09-10 02:39:07]

Patchset 1 (id:??) landed as
https://crrev.com/12c173d02d9306bdd180a4535d55aabf581b4c33
Cr-Commit-Position: refs/heads/master@{#291804}