Fix WebstoreInlineInstaller ASAN bugs

Certain code paths which called back onto a raw pointer to a
WebstoreInlineInstaller could not guarantee the object's existence at
callback time.

Additional ref counts have been added to ensure that this is no longer the case.

BUG=236513,241431,241432,247774,263004

Review URL: https://codereview.chromium.org/24839002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228239 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228239