Expose SkComposeShader as SK_API.

This is used by the ChromeOS build of Chrome.
Review URL: http://codereview.appspot.com/4548054

git-svn-id: http://skia.googlecode.com/svn/trunk@1396 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/core/SkComposeShader.h b/include/core/SkComposeShader.h
index 0b198f6..ea37549 100644
--- a/include/core/SkComposeShader.h
+++ b/include/core/SkComposeShader.h
@@ -27,7 +27,7 @@
     This subclass of shader returns the coposition of two other shaders, combined by
     a xfermode.
 */
-class SkComposeShader : public SkShader {
+class SK_API SkComposeShader : public SkShader {
 public:
     /** Create a new compose shader, given shaders A, B, and a combining xfermode mode.
         When the xfermode is called, it will be given the result from shader A as its