Add asserts to catch missing deoptimization info early.

runtime/vm/code_patcher.cc

Index: runtime/vm/code_patcher.cc
===================================================================
--- runtime/vm/code_patcher.cc	(revision 20298)
+++ runtime/vm/code_patcher.cc	(working copy)
@@ -28,6 +28,7 @@
 void CodePatcher::PatchEntry(const Code& code) {
   const uword patch_addr = code.GetPcForDeoptId(Isolate::kNoDeoptId,
                                                 PcDescriptors::kEntryPatch);
+  ASSERT(patch_addr != 0);
   JumpPattern jmp_entry(patch_addr);
   ASSERT(!jmp_entry.IsValid());
   const uword patch_buffer = code.GetPatchCodePc();
@@ -47,6 +48,7 @@
 void CodePatcher::RestoreEntry(const Code& code) {
   const uword patch_addr = code.GetPcForDeoptId(Isolate::kNoDeoptId,
                                                 PcDescriptors::kEntryPatch);
+  ASSERT(patch_addr != 0);
   JumpPattern jmp_entry(patch_addr);
   ASSERT(jmp_entry.IsValid());
   const uword jump_target = jmp_entry.TargetAddress();