Release partially constructed GLES2 implementation in Pepper Graphics3D resource.
Remove a guard which prevents destruction of the GLES2 implementation in cases
where an error causes only partial construction. Otherwise, the CommandBufferHelper
destructor will access the CommandBuffer after it has been destroyed.

BUG=285578

Review URL: https://codereview.chromium.org/25590002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226354 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226354