views: Make view::Views::GetPreferredSize() const.

Due to button refactoring patches, we now need to ask views for their
preferred sizes in const methods. Across the entire codebase, the
overwhelming majority of GetPreferredSize() implementations could be
const. There are only a few places where we can't, and they are usually
combining the sizing and layout code.

BookmarksBarView was simple enough to perform this separation. Most of
the other places were solved by adding "mutable" to value caches.

BUG=155363
[email protected], [email protected], [email protected], [email protected], pkasting, sky
TBR=jam, scheib

Review URL: https://codereview.chromium.org/273223002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271682 0039d316-1c4b-4281-b951-d872f2087c98
400 files changed