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/tests.gyp b/gyp/tests.gyp
index 890a146..841baf7 100644
--- a/gyp/tests.gyp
+++ b/gyp/tests.gyp
@@ -12,6 +12,7 @@
         '../src/effects',
         '../src/image',
         '../src/lazy',
+        '../src/images',
         '../src/pathops',
         '../src/pdf',
         '../src/pipe/utils',