Don't dereference null pointer in FastTextAutosizer::getTentativeClusterRoots()

Don't dereference null pointer in FastTextAutosizer::getTentativeClusterRoots()

The result of m_blocksForFingerprint.get() can be a null pointer, so don't
dereference it (that invokes undefined behaviour). Instead, just return the pointer.

Recent versions of Clang will optimize based on references always pointing
to valid objects. In the previous code below:

  BlockSet* roots = m_fingerprintMapper.getTentativeClusterRoots(fingerprint);
  if (!roots || roots->size() < 2 || !roots->contains(block))
      return 0;

the "!roots" null check would be optimized away, since "roots" is the address
of a reference, and must therefore point to a valid object.

BUG=38149
TEST=fast/text-autosizing tests don't crash with new Clang

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179171

[hans, 2014-07-29 17:39:27]

Please take a look.

[Nico, 2014-07-29 17:43:07]

lgtm

[pdr., 2014-07-29 17:56:08]

On 2014/07/29 17:43:07, Nico (away) wrote:
> lgtm

LGTM2

[pdr., 2014-07-29 17:56:13]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2014-07-29 17:56:44]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hans@chromium.org/418253003/1

[commit-bot: I haz the power, 2014-07-29 20:06:48]

Change committed as 179171