Create libffmpeg.so in the component build.

ffmpeg.gyp

Index: ffmpeg.gyp
===================================================================
--- ffmpeg.gyp	(revision 98555)
+++ ffmpeg.gyp	(working copy)
@@ -458,7 +458,7 @@
             'intermediate_dir': '<(INTERMEDIATE_DIR)',
             'output_root': '<(SHARED_INTERMEDIATE_DIR)/ffmpeg',
           },
-          'type': '<(library)',
+          'type': '<(component)',
           'include_dirs': [
             '<(output_root)',
             '../..',  # The chromium 'src' directory.
@@ -509,6 +509,10 @@
               },
             }],
 
+            ['component=="shared_library"', {
+              'cflags!': ['-fvisibility=hidden'],
+            }],
+
             # Add pkg-config result to include path when use_system_ffmpeg!=0
             ['use_system_ffmpeg!=0', {
               'cflags': [