Add the lazy decoder from PictureFlags to SkImageDecoder

include/core/SkImageDecoder.h

Index: include/core/SkImageDecoder.h
diff --git a/include/core/SkImageDecoder.h b/include/core/SkImageDecoder.h
index 191fe53f4c588a0584486fee25b68ee7a2c7ab1f..8cb4881b40e7a139c7e029fff9249fc56e24e7cd 100644
--- a/include/core/SkImageDecoder.h
+++ b/include/core/SkImageDecoder.h
@@ -13,6 +13,7 @@
 #include "SkBitmap.h"
 #include "SkBitmapFactory.h"
 #include "SkImage.h"
+#include "SkLruImageCache.h"
 #include "SkRect.h"
 #include "SkRefCnt.h"
 #include "SkTypes.h"
@@ -97,6 +98,13 @@ public:
     */
     bool getRequireUnpremultipliedColors() const { return fRequireUnpremultipliedColors; }
 
+    /**
+     * Returns a pointer to the LRU cache used by LazyDecodeBitmap.
+     */
+    static SkLruImageCache* getLruImageCache() {

[scroggo, 2013/07/15 15:09:28]

This does not generally relate to SkImageDecoder, so I don't think that it
belongs here.

+        return &fLruImageCache;

[scroggo, 2013/07/15 15:09:28]

SkImageDecoder.h is built by chromium, but SkImageDecoder.cpp is not (instead,
it builds SkImageDecoder_empty.cpp, because it does not use SkImageDecoder, but
some of our other files depend on it). This means that this static variable
(which chromium tries to avoid anyway) won't get initialized.

+    }
+
     /** \class Peeker
 
         Base class for optional callbacks to retrieve meta/chunk data out of
@@ -308,6 +316,11 @@ public:
     }
 
     /**
+     * Decode the image with DecodeMemoryToTarget but defer the process until it is needed.
+     */
+    static bool LazyDecodeBitmap(const void* buffer, size_t size, SkBitmap* bitmap);

[scroggo, 2013/07/15 15:09:28]

I support moving LazyDecodeBitmap to a header file for documentation/ease of
access, but I don't think SkImageDecoder is the right place for it.

Although it uses SkImageDecoder, SkImageDecoder does not use it, so it could
easily live in its own file(s).

I lean towards leaving the files in tools/ until/unless we decide to make it
public. LazyDecodeBitmap is only used by our tools, and may undergo some changes
before we get our clients to use it.

+
+    /**
      *  Decode memory.
      *  @param info Output parameter. Returns info about the encoded image.
      *  @param target Contains the address of pixel memory to decode into
@@ -468,6 +481,10 @@ private:
     mutable bool            fShouldCancelDecode;
     bool                    fPreferQualityOverSpeed;
     bool                    fRequireUnpremultipliedColors;
+
+    static SkLruImageCache fLruImageCache;
+    static SkBitmapFactory fLazyBitmapFactory;
+
 };
 
 /** Calling newDecoder with a stream returns a new matching imagedecoder