This patch refactors SVGPatternElement::collectPatternAttributes() by extracting
the setPatternAttributes logic into a new function. This patch also changes the
while loop to be easier to understand and similar to collectGradientAttributes.

A similar refactoring was done to collectGradientAttributes in r165358 [1].

[1] https://src.chromium.org/viewvc/blink?view=rev&revision=165358

BUG=N/A

Review URL: https://codereview.chromium.org/137533021

git-svn-id: svn://svn.chromium.org/blink/trunk@165427 bbb929c8-8fbe-4397-9dbb-9b2b20218538