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Cubic bezier timing functions are based on two knots (x1, y1) and (x2, y2) (the
other knots are assumed to be (0, 0) and (1, 1)). We require that x1, x2 lie
within (0, 1) (so that the bezier does not 'fold back' on itself), but y1, and
y2 should have no such constraint. They currently do. This CL reimplements
bezier interpolation without this restriction. This interpolation has two steps:
   1) Find the t corresponding to the desired x.
   2) Interpolate y's at the t computed in step 1.
Step 1 is an iterative minimization. Here I do bisection for simplicity, but I
could take Newton steps if this turns out to be a bottleneck.

R=ajuma@chromium.org
BUG=178070

Review URL: https://chromiumcodereview.appspot.com/16112002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202755 0039d316-1c4b-4281-b951-d872f2087c98