Support %_IsObject in Crankshaft.

src/arm/lithium-codegen-arm.h

Index: src/arm/lithium-codegen-arm.h
===================================================================
--- src/arm/lithium-codegen-arm.h	(revision 5982)
+++ src/arm/lithium-codegen-arm.h	(working copy)
@@ -208,6 +208,15 @@
   Condition EmitTypeofIs(Label* true_label, Label* false_label,
                          Register input, Handle<String> type_name);
 
+  // Emits optimized code for %_IsObject(x).  Preserves input register.
+  // Returns the condition on which a final split to
+  // true and false label should be made, to optimize fallthrough.
+  Condition EmitIsObject(Register input,
+                         Register temp1,
+                         Register temp2,
+                         Label* is_not_object,
+                         Label* is_object);
+
   LChunk* const chunk_;
   MacroAssembler* const masm_;
   CompilationInfo* const info_;