X87: Add a MathFloor stub generated with TurboFan

port  abc35080 (r28339)

original commit message:

    This stub will be used as the basis of a Math.floor-specific CallIC to
    detect and track calls to floor that return -0.

    Along the way:
    - Create a TurboFanCodeStub super class from which the StringLength and
    MathRound TF stubs derive.
    - Fix the ugly hack that passes the first stub parameter as the "this"
    pointer in the the TF-compiled JS function.
    - Fix bugs in the ia32/x64 disassembler.

BUG=

Review URL: https://codereview.chromium.org/1134323002

Cr-Commit-Position: refs/heads/master@{#28386}

src/x87/disasm-x87.cc

@@ -1292,7 +1292,7 @@ int DisassemblerX87::InstructionDecode(v8::internal::Vector<char> out_buffer,
             } else if (*data == 0x16) {
               data++;
               int mod, regop, rm;
-              get_modrm(*data, &mod, &regop, &rm);
+              get_modrm(*data, &mod, &rm, &regop);
               int8_t imm8 = static_cast<int8_t>(data[1]);
               AppendToBuffer("pextrd %s,%s,%d",
                              NameOfCPURegister(regop),

src/x87/interface-descriptors-x87.cc

@@ -370,6 +370,21 @@ void ApiAccessorDescriptor::Initialize(CallInterfaceDescriptorData* data) {
   };
   data->Initialize(arraysize(registers), registers, representations);
 }
+
+
+void MathRoundVariantDescriptor::Initialize(CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      esi,  // context
+      edi,  // math rounding function
+      edx,  // vector slot id
+  };
+  Representation representations[] = {
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+      Representation::Tagged(),  //
+  };
+  data->Initialize(arraysize(registers), registers, representations);
+}
 }
 }  // namespace v8::internal