[#8] Pass gfx::Point by const ref.

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 and some
other scenarios mentioned in the bug.

BUG=159273

Review URL: https://codereview.chromium.org/185653013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255025 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255025