Add SkImageGenerator Interface

-   Add SkDiscardablePixelRef class that uses SkDiscardableMemory and
    a SkImageGenerator.

-   Add SkDecodingImageGenerator class as an example of a
    SkImageGenerator.

-   Add DecodingImageGenerator unit test.

-   Add SkBasicDiscardableMemory implmentation for unit tests only.

R=reed@google.com, scroggo@google.com

Review URL: https://codereview.chromium.org/74793011

git-svn-id: http://skia.googlecode.com/svn/trunk@12341 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/core.gypi b/gyp/core.gypi
index e31b8ff..54e23ef 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -73,6 +73,7 @@
         '<(skia_src_path)/core/SkDevice.cpp',
         '<(skia_src_path)/core/SkDeviceLooper.cpp',
         '<(skia_src_path)/core/SkDeviceProfile.cpp',
+        '<(skia_src_path)/lazy/SkDiscardablePixelRef.cpp',
         '<(skia_src_path)/core/SkDither.cpp',
         '<(skia_src_path)/core/SkDraw.cpp',
         '<(skia_src_path)/core/SkDrawLooper.cpp',