Add AlphaThreshold filter.

This is based on the Bitmap Alpha Threshold filter, and will be used by Chromium
to implement the window shape API.

R=bsalomon@chromium.org, wez@chromium.org, bsalomon@google.com, reed@google.com

Author: zork@chromium.org

Review URL: https://codereview.chromium.org/115633002

git-svn-id: http://skia.googlecode.com/svn/trunk@12935 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/effects.gypi b/gyp/effects.gypi
index 74cfdda..21e02e4 100644
--- a/gyp/effects.gypi
+++ b/gyp/effects.gypi
@@ -9,6 +9,7 @@
   'sources': [
     '<(skia_src_path)/effects/Sk1DPathEffect.cpp',
     '<(skia_src_path)/effects/Sk2DPathEffect.cpp',
+    '<(skia_src_path)/effects/SkAlphaThresholdFilter.cpp',
     '<(skia_src_path)/effects/SkArithmeticMode.cpp',
     '<(skia_src_path)/effects/SkAvoidXfermode.cpp',
     '<(skia_src_path)/effects/SkBicubicImageFilter.cpp',
@@ -80,6 +81,7 @@
     '<(skia_include_path)/effects/Sk1DPathEffect.h',
     '<(skia_include_path)/effects/Sk2DPathEffect.h',
     '<(skia_include_path)/effects/SkXfermodeImageFilter.h',
+    '<(skia_include_path)/effects/SkAlphaThresholdFilter.h',
     '<(skia_include_path)/effects/SkArithmeticMode.h',
     '<(skia_include_path)/effects/SkAvoidXfermode.h',
     '<(skia_include_path)/effects/SkBitmapSource.h',
diff --git a/gyp/gmslides.gypi b/gyp/gmslides.gypi
index 40eb101..8e50eb0 100644
--- a/gyp/gmslides.gypi
+++ b/gyp/gmslides.gypi
@@ -73,6 +73,7 @@
     '../gm/hairlines.cpp',
     '../gm/hairmodes.cpp',
     '../gm/hittestpath.cpp',
+    '../gm/imagealphathreshold.cpp',
     '../gm/imageblur.cpp',
     '../gm/imagemagnifier.cpp',
     '../gm/inversepaths.cpp',
diff --git a/gyp/public_headers.gypi b/gyp/public_headers.gypi
index a9ef4dd..b42623f 100644
--- a/gyp/public_headers.gypi
+++ b/gyp/public_headers.gypi
@@ -72,6 +72,7 @@
       'effects/SkMorphologyImageFilter.h',
       'effects/Sk2DPathEffect.h',
       'effects/SkXfermodeImageFilter.h',
+      'effects/SkAlphaThresholdFilter.h',
       'effects/SkArithmeticMode.h',
       'effects/SkMergeImageFilter.h',
       'effects/SkPerlinNoiseShader.h',