Disable ReadWriteAlpha test on Android

Failing on Nexus 7

Bug: http://code.google.com/p/skia/issues/detail?id=753
Review URL: https://codereview.appspot.com/6455077

git-svn-id: http://skia.googlecode.com/svn/trunk@4921 2bbb7eff-a529-9590-31e7-b0007b416f81

tests/ReadWriteAlphaTest.cpp

@@ -105,7 +105,9 @@ static void ReadWriteAlphaTest(skiatest::Reporter* reporter, GrContext* context)
     REPORTER_ASSERT(reporter, match);
 }
 
+#ifndef SK_BUILD_FOR_ANDROID
 #include "TestClassDef.h"
 DEFINE_GPUTESTCLASS("ReadWriteAlpha", ReadWriteAlphaTestClass, ReadWriteAlphaTest)
 
 #endif
+#endif