Fix gradient pattern tiling for tile sizes greater than 32k

This fix works around a limitation of SkBitmapProcShader by avoiding
to cache gradient patterns in bitmaps when the bitmap would be more
that 32k wide or high.

New layout tests verify the vertically and horizontally oriented
gradient using a border to triger a phase shift in the pattern, which
activates the pattern tiling code path.

Note: The correctness of GeneratorGeneratedImage::drawPatternWithoutCache
was verified by running gradient layout tests with
MAX_PATTERN_TILE_SIZE set to 0.

BUG=241486

Review URL: https://chromiumcodereview.appspot.com/18328019

git-svn-id: svn://svn.chromium.org/blink/trunk@153579 bbb929c8-8fbe-4397-9dbb-9b2b20218538