Implement ARM disassembler.

runtime/vm/instructions_arm_test.cc

Index: runtime/vm/instructions_arm_test.cc
===================================================================
--- runtime/vm/instructions_arm_test.cc	(revision 18767)
+++ runtime/vm/instructions_arm_test.cc	(working copy)
@@ -16,12 +16,13 @@
 
 ASSEMBLER_TEST_GENERATE(Call, assembler) {
   __ BranchLinkPatchable(&StubCode::InstanceFunctionLookupLabel());
-  __ Stop("Test should not be executed");
+  // Do not emit any code after the call above, since we decode backwards
+  // starting from the return address, i.e. from the end of this code buffer.
 }
 
 
 ASSEMBLER_TEST_RUN(Call, test) {
-  CallPattern call(test->entry(), test->code());
+  CallPattern call(test->entry() + test->code().Size(), test->code());
   EXPECT_EQ(StubCode::InstanceFunctionLookupLabel().address(),
             call.TargetAddress());
 }