Sk_API for SkImageGenerator and SkInstallDiscardablePixelRef

Added SK_API to SkImageGenerator (already in include/).

Moved SkDiscardablePixelRef::Install to SkInstallDiscardablePixelRef,
added SK_API to that function, and moved declaration to
SkImageGenerator.h

This keeps the SkDiscardablePixelRef internal to Skia, but exposes a
method to install it into a bitmap.

Modifed tests that rely on this functio to use new version.

BUG=
R=mtklein@google.com, reed@google.com

Review URL: https://codereview.chromium.org/111713002

git-svn-id: http://skia.googlecode.com/svn/trunk@12612 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/DrawBitmapRectTest.cpp b/tests/DrawBitmapRectTest.cpp
index 9289e11..642e2ce 100644
--- a/tests/DrawBitmapRectTest.cpp
+++ b/tests/DrawBitmapRectTest.cpp
@@ -10,7 +10,7 @@
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkDiscardableMemoryPool.h"
-#include "SkDiscardablePixelRef.h"
+#include "SkImageGenerator.h"
 #include "SkPaint.h"
 #include "SkShader.h"
 #include "SkSurface.h"
@@ -48,7 +48,7 @@
     SkAutoTUnref<SkDiscardableMemoryPool> pool(SkNEW_ARGS(SkDiscardableMemoryPool,
                                                           (10 * 1000, NULL)));
     SkBitmap bm;
-    bool installSuccess = SkDiscardablePixelRef::Install(SkNEW(FailureImageGenerator), &bm, pool);
+    bool installSuccess = SkInstallDiscardablePixelRef(SkNEW(FailureImageGenerator), &bm, pool);
     REPORTER_ASSERT(reporter, installSuccess);
     // now our bitmap has a pixelref, but we know it will fail to lock