Fix null dereference on MemoryCache.

Fix null dereference on MemoryCache.

Usually a valid MemoryCacheEntry holds a non-null Resource as |m_resource|. But
when we hold a valid MemoryCacheEntry beyond destructive statements, it may be
evicted from the cache and get stale. That means |m_resource| can be null in
such cases. This CL checks it in order to avoid null dereference.

BUG=488373
Review URL: https://codereview.chromium.org/1537343002

Cr-Commit-Position: refs/heads/master@{#367802}
(cherry picked from commit 843010ff7eeda6e9e87347aaaa6365efecd1161d)

Committed: https://chromium.googlesource.com/chromium/src/+/9f80eae6508185f7aed39f1f91a301d9ca18978a

[yhirano, 2016-01-12 08:54:07]

Description was changed from

==========
Fix null dereference on MemoryCache.

Usually a valid MemoryCacheEntry holds a non-null Resource as |m_resource|. But
when we hold a valid MemoryCacheEntry beyond destructive statements, it may be
evicted from the cache and get stale. That means |m_resource| can be null in
such cases. This CL checks it in order to avoid null dereference.

BUG=488373

Review URL: https://codereview.chromium.org/1537343002

Cr-Commit-Position: refs/heads/master@{#367802}
(cherry picked from commit 843010ff7eeda6e9e87347aaaa6365efecd1161d)
==========

to

==========
Fix null dereference on MemoryCache.

Usually a valid MemoryCacheEntry holds a non-null Resource as |m_resource|. But
when we hold a valid MemoryCacheEntry beyond destructive statements, it may be
evicted from the cache and get stale. That means |m_resource| can be null in
such cases. This CL checks it in order to avoid null dereference.

BUG=488373

Review URL: https://codereview.chromium.org/1537343002

Cr-Commit-Position: refs/heads/master@{#367802}
(cherry picked from commit 843010ff7eeda6e9e87347aaaa6365efecd1161d)

Committed:
https://chromium.googlesource.com/chromium/src/+/9f80eae6508185f7aed39f1f91a3...
==========

[yhirano, 2016-01-12 08:54:10]

Committed patchset #1 (id:1) manually as
9f80eae6508185f7aed39f1f91a301d9ca18978a.

[yhirano, 2016-01-13 02:16:54]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1576423005/ by yhirano@chromium.org.

The reason for reverting is: The change broke beta builds..