Fix some ArtMethod related bugs

Added root visiting for runtime methods, not currently required
since the GcRoots in these methods are null.

Added missing GetInterfaceMethodIfProxy in GetMethodLine, fixes
--trace run-tests 005, 044.

Fixed optimizing compiler bug where we used a normal stack location
instead of double on ARM64, this fixes the debuggable tests.

TODO: Fix JDWP tests.

Bug: 19264997

Change-Id: I7c55f69c61d1b45351fd0dc7185ffe5efad82bd3
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index fbe26b0..40432e4 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -637,7 +637,7 @@
   DCHECK_NE(type, Primitive::kPrimVoid);
 
   if (instruction->IsCurrentMethod()) {
-    MoveLocation(location, Location::StackSlot(kCurrentMethodStackOffset));
+    MoveLocation(location, Location::DoubleStackSlot(kCurrentMethodStackOffset));
   } else if (locations != nullptr && locations->Out().Equals(location)) {
     return;
   } else if (instruction->IsIntConstant()