MIPS: Fix for instanceof-proxies failure.

Invalidate the instanceof cache in proxy-case of InstanceOfStub
after the changes in https://codereview.chromium.org/1492243003.

This didn't have a test case until https://codereview.chromium.org/1518773003

TEST=mjsunit/es6/instanceof-proxies.js
BUG=

Review URL: https://codereview.chromium.org/1519303002

Cr-Commit-Position: refs/heads/master@{#32821}

src/mips/code-stubs-mips.cc

@@ -1529,6 +1529,9 @@ void InstanceOfStub::Generate(MacroAssembler* masm) {
   // Proxy-case: Call the %HasInPrototypeChain runtime function.
   __ bind(&proxy_case);
   __ Push(object, function_prototype);
+  // Invalidate the instanceof cache.
+  DCHECK(Smi::FromInt(0) == 0);
+  __ StoreRoot(zero_reg, Heap::kInstanceofCacheFunctionRootIndex);
   __ TailCallRuntime(Runtime::kHasInPrototypeChain, 2, 1);
 
   // Slow-case: Call the %InstanceOf runtime function.

src/mips64/code-stubs-mips64.cc

@@ -1531,6 +1531,9 @@ void InstanceOfStub::Generate(MacroAssembler* masm) {
   // Proxy-case: Call the %HasInPrototypeChain runtime function.
   __ bind(&proxy_case);
   __ Push(object, function_prototype);
+  // Invalidate the instanceof cache.
+  DCHECK(Smi::FromInt(0) == 0);
+  __ StoreRoot(zero_reg, Heap::kInstanceofCacheFunctionRootIndex);
   __ TailCallRuntime(Runtime::kHasInPrototypeChain, 2, 1);
 
   // Slow-case: Call the %InstanceOf runtime function.