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/tools/LazyDecodeBitmap.cpp b/tools/LazyDecodeBitmap.cpp
index f5ff147..9a4a36f 100644
--- a/tools/LazyDecodeBitmap.cpp
+++ b/tools/LazyDecodeBitmap.cpp
@@ -10,7 +10,7 @@
 #include "SkData.h"
 #include "SkDecodingImageGenerator.h"
 #include "SkDiscardableMemoryPool.h"
-#include "SkDiscardablePixelRef.h"
+#include "SkImageGenerator.h"
 #include "SkForceLinking.h"
 
 #include "SkCommandLineFlags.h"
@@ -44,5 +44,5 @@
         // Only meaningful if platform has a default discardable
         // memory implementation that differs from the global DM pool.
     }
-    return SkDiscardablePixelRef::Install(gen.detach(), dst, pool);
+    return SkInstallDiscardablePixelRef(gen.detach(), dst, pool);
 }