Fixed two register allocator bugs (off-by-one error/failure propagation).

src/lithium-allocator.h

Index: src/lithium-allocator.h
diff --git a/src/lithium-allocator.h b/src/lithium-allocator.h
index 2ca853763e893343bf01315f2dafbfd5018c43d5..0e24d54dc47cc9803f44496b3f6ab484a27124b5 100644
--- a/src/lithium-allocator.h
+++ b/src/lithium-allocator.h
@@ -427,8 +427,10 @@ class LAllocator BASE_EMBEDDED {
   Zone* zone() const { return zone_; }
 
   int GetVirtualRegister() {
-    if (next_virtual_register_ > LUnallocated::kMaxVirtualRegisters) {
+    if (next_virtual_register_ >= LUnallocated::kMaxVirtualRegisters) {
       allocation_ok_ = false;
+      // Maintain the invariant that we return something below the maximum.
+      return 0;
     }
     return next_virtual_register_++;
   }