Add geometry-based rotated AA rect drawing path

This is a somewhat speculative attempt to address this regression: https://code.google.com/p/chromium/issues/detail?id=180345.

On Win7 (old on left; new on right) we get (removing any differences <= .5ms or <= 3%):
         
                 rects_1_stroke_4 GPU c     0.78    1.40      -0.62   -79.5% 
bitmap_8888_A_scale_rotate_filter GPU c     1.40    2.34      -0.94   -67.1% 
       path_stroke_small_triangle GPU c    26.83   28.55      -1.72    -6.4% 
                          readpix GPU c    79.25   84.08      -4.83    -6.1% 
             giantdashline_vert_2 GPU c    13.42   14.20      -0.78    -5.8% 
             giantdashline_hori_0 GPU c    12.95   13.57      -0.62    -4.8% 
         path_fill_small_sawtooth GPU c    16.54   17.32      -0.78    -4.7% 
           path_stroke_small_rect GPU c    25.27   26.21      -0.94    -3.7% 
                          polygon GPU c    51.48   53.20      -1.72    -3.3% 

        path_fill_small_long_line GPU c    20.12   19.50      +0.62    +3.1% 
               bitmap_8888_update GPU c    41.50   40.09      +1.41    +3.4% 
                   aaclip_rect_AA GPU c    18.56   17.78      +0.78    +4.2% 
  bitmap_8888_update_scale_filter GPU c    43.37   41.50      +1.87    +4.3% 
             giantdashline_hori_2 GPU c    42.74   40.56      +2.18    +5.1% 
                matrixconvolution GPU c    11.08   10.30      +0.78    +7.0% 
          blurrect_boxfilter_1.50 GPU c     8.58    7.80      +0.78    +9.1% 
                       maskshader GPU c     3.28    2.65      +0.63   +19.2% 
   lightingpointlitspecular_large GPU c     1.09    0.47      +0.62   +56.9% 
                  aarects_rotated GPU c   113.41   22.31     +91.10   +80.3% 

Of these times I believe only the 'aarects_rotated' difference is real.

For SampleApp::ManyRects (with rotations and AA turned on and clipping turned off) we get:

without Opt: ~2ms
with Opt:    ~1ms

[bsalomon, 2013-05-02 15:33:09]

On 2013/05/02 15:08:27, robertphillips wrote:

lgtm

[robertphillips, 2013-05-02 17:13:29]

committed as r8961