Add locks in test ResourceProviderContext for TestTexture objects.

The lock in TestWebGraphicsContext3D::namespace_ is supposed to protect all fields in the namespace.

Before, we were locking when we accessed the namespace_->textures object. However, we should also be locking when we access the individual TestTexture objects in namespace_->textures.

Review URL: https://codereview.chromium.org/29473002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230145 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230145