Follow the design guidelines for the AArch64 `EmissionCheckScope`.

It uses a newly defined `MacroAssemblerInterface` class.

Change-Id: I10ba663ec047d1ea320610bc2d5565de24d9686b
diff --git a/src/macro-assembler-interface.h b/src/macro-assembler-interface.h
new file mode 100644
index 0000000..22434de
--- /dev/null
+++ b/src/macro-assembler-interface.h
@@ -0,0 +1,45 @@
+// Copyright 2016, VIXL authors
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//   * Redistributions of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//   * Redistributions in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//   * Neither the name of ARM Limited nor the names of its contributors may be
+//     used to endorse or promote products derived from this software without
+//     specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS CONTRIBUTORS "AS IS" AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
+// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef VIXL_MACRO_ASSEMBLER_INTERFACE_H
+#define VIXL_MACRO_ASSEMBLER_INTERFACE_H
+
+#include "assembler-base-vixl.h"
+
+namespace vixl {
+
+class MacroAssemblerInterface {
+ public:
+  virtual internal::AssemblerBase* GetAssemblerBase() = 0;
+
+  virtual void BlockPools() = 0;
+  virtual void ReleasePools() = 0;
+  virtual void EnsureEmitPoolsFor(size_t size) = 0;
+};
+
+}  // namespace vixl
+
+#endif  // VIXL_MACRO_ASSEMBLER_INTERFACE_H