Pass gfx structs by const ref (gfx::Vector2d)

      Avoid unneccessary copy of structures gfx::Vector2d
by passing them by const ref rather than value.

Any struct of size > 4 bytes should be passed by const ref.
Passing by ref for these structs is faster than passing
by value, especially when invoking function has multiple parameters.


Pass gfx structs by const ref (gfx::Vector2d)

BUG=159273

Review URL: https://codereview.chromium.org/132163009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248941 0039d316-1c4b-4281-b951-d872f2087c98