Have SkVarAlloc::alloc() use sk_malloc_throw.

tests/VarAllocTest.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
 #include "Test.h"
 #include "SkVarAlloc.h"
 
 DEF_TEST(VarAlloc, r) {
     SkVarAlloc va(4/*start allocating at 16B*/);
-    char* p = va.alloc(128, SK_MALLOC_THROW);
+    char* p = va.alloc(128);
     sk_bzero(p, 128);  // Just checking this is safe.
 
 #if !defined(SK_BUILD_FOR_ANDROID) && !defined(__UCLIBC__)
     // This method will always return 0 on Android and UCLIBC platforms.
     REPORTER_ASSERT(r, va.approxBytesAllocated() >= 128);
 #endif
 }