Include gif image decoding in images/ on linux.

Build SkImageDecoder_libgif in images project and link against
libgif on linux.

Ensure that the GIF decoder is used in skimage.

Requires a new dependency on libgif-dev when building on linux.

Review URL: https://codereview.chromium.org/14029011

git-svn-id: http://skia.googlecode.com/svn/trunk@8627 2bbb7eff-a529-9590-31e7-b0007b416f81

gyp/images.gyp

@@ -97,12 +97,7 @@
           ],
         }],
         [ 'skia_os in ["linux", "freebsd", "openbsd", "solaris", "nacl"]', {
-          'sources!': [
-            '../src/images/SkImageDecoder_libgif.cpp',
-            '../src/images/SkMovie_gif.cpp',
-          ],
-          # libpng stuff:
-          # Any targets that depend on this target should link in libpng and
+          # Any targets that depend on this target should link in libpng, libgif, and
           # our code that calls it.
           # See http://code.google.com/p/gyp/wiki/InputFormatReference#Dependent_Settings
           'link_settings': {
@@ -110,11 +105,12 @@
               '../src/images/SkImageDecoder_libpng.cpp',
             ],
             'libraries': [
+              '-lgif',
               '-lpng',
               '-lz',
             ],
           },
-          # end libpng stuff
+          # end libpng/libgif stuff
         }],
         [ 'skia_os == "android"', {
           'include_dirs': [

tools/skimage_main.cpp

@@ -159,8 +159,15 @@ int tool_main(int argc, char** argv) {
 void forceLinking();
 
 void forceLinking() {
+    // This function leaks, but that is okay because it is not intended
+    // to be called. It is only here so that the linker will include the
+    // decoders.
     SkDEBUGCODE(SkImageDecoder *creator = ) CreateJPEGImageDecoder();
     SkASSERT(creator);
+#ifdef SK_BUILD_FOR_UNIX
+    SkDEBUGCODE(creator = ) CreateGIFImageDecoder();
+    SkASSERT(creator);
+#endif
 }
 
 #if !defined SK_BUILD_FOR_IOS