[asm-cherry-pick] Use MethodWriter to compute maxLocals / maxStack

Make class MethodWriter public and add accessors for maxLocals and
maxStack. This is the simplest way to compute the maxs using the
ASM framework. It is used in the optimizer, see
scala/scala@90781e8

Cherry-pick of
lrytz/scala@91810c9

Author: lrytz

src/main/java/scala/tools/asm/MethodWriter.java

@@ -37,7 +37,7 @@
  * @author Eric Bruneton
  * @author Eugene Kuleshov
  */
-class MethodWriter extends MethodVisitor {
+public class MethodWriter extends MethodVisitor {
 
     /**
      * Pseudo access flag used to denote constructors.
@@ -235,11 +235,19 @@ class MethodWriter extends MethodVisitor {
      */
     private int maxStack;
 
+    public int getMaxStack() {
+        return maxStack;
+    }
+
     /**
      * Maximum number of local variables for this method.
      */
     private int maxLocals;
 
+    public int getMaxLocals() {
+        return maxLocals;
+    }
+
     /**
      * Number of local variables in the current stack map frame.
      */