Fixes for JPEG subset decoding.

Ensure that the stream passed to JPEG for subset decoding is
neither deleted before it is no longer needed nor deleted an
extra time.

src/images/SkJpegUtility.h:
src/images/SkJpegUtility.cpp:
Always ref and unref the stream provided to skjpeg_source_mgr.
Add some comments explaining how skjpeg_source_mgr's members
handle ownership.
Fix a warning comparing signed and unsigned numbers, converting
to size_t which is more appropriate for measuring bytes.
Remove dead code referring to fMemoryBase and fMemoryBaseSize,
which are never used.

src/images/SkImageDecoder_libjpeg.cpp:
Call the new constructor for skjpeg_source_mgr, which no longer
takes a boolean to determine ownership.

include/images/SkBitmapRegionDecoder.h
src/images/SkBitmapRegionDecoder.cpp:
This small shim has been removed, since it is not needed to use
Skia's image decoders. Its functionality will be folded into
Android.

Required for the merge to Android.

R=djsollen@google.com

Review URL: https://codereview.chromium.org/21561002

git-svn-id: http://skia.googlecode.com/svn/trunk@10483 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/images/SkImageDecoder_libjpeg.cpp b/src/images/SkImageDecoder_libjpeg.cpp
index e0783c9..81904ae 100644
--- a/src/images/SkImageDecoder_libjpeg.cpp
+++ b/src/images/SkImageDecoder_libjpeg.cpp
@@ -65,7 +65,7 @@
 class SkJPEGImageIndex {
 public:
     SkJPEGImageIndex(SkStream* stream, SkImageDecoder* decoder)
-        : fSrcMgr(stream, decoder, true) {}
+        : fSrcMgr(stream, decoder) {}
 
     ~SkJPEGImageIndex() {
 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
@@ -238,7 +238,7 @@
 
     jpeg_decompress_struct  cinfo;
     skjpeg_error_mgr        errorManager;
-    skjpeg_source_mgr       srcManager(stream, this, false);
+    skjpeg_source_mgr       srcManager(stream, this);
 
     cinfo.err = jpeg_std_error(&errorManager);
     errorManager.error_exit = skjpeg_error_exit;