[arm] Clean up use of IsSupported and IsEnabled.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 77beac12a2b984272e9408a5cf4f11d29c874235..acd77e45eb6e5896b6d7038703ecc3d6cb48e24c 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -80,9 +80,14 @@ class AssemblerBase: public Malloced {
   void set_enabled_cpu_features(uint64_t features) {
     enabled_cpu_features_ = features;
   }
+  // Features are usually enabled by CpuFeatureScope, which also asserts that
+  // the features are supported before they are enabled.
   bool IsEnabled(CpuFeature f) {
     return (enabled_cpu_features_ & (static_cast<uint64_t>(1) << f)) != 0;
   }
+  void EnableCpuFeature(CpuFeature f) {
+    enabled_cpu_features_ |= (static_cast<uint64_t>(1) << f);
+  }
 
   bool is_constant_pool_available() const {
     if (FLAG_enable_embedded_constant_pool) {
@@ -184,15 +189,22 @@ class PredictableCodeSizeScope {
 // Enable a specified feature within a scope.
 class CpuFeatureScope BASE_EMBEDDED {
  public:
+  enum CheckPolicy {
+    kCheckSupported,
+    kDontCheckSupported,
+  };
+
 #ifdef DEBUG
-  CpuFeatureScope(AssemblerBase* assembler, CpuFeature f);
+  CpuFeatureScope(AssemblerBase* assembler, CpuFeature f,
+                  CheckPolicy check = kCheckSupported);
   ~CpuFeatureScope();
 
  private:
   AssemblerBase* assembler_;
   uint64_t old_enabled_;
 #else
-  CpuFeatureScope(AssemblerBase* assembler, CpuFeature f) {}
+  CpuFeatureScope(AssemblerBase* assembler, CpuFeature f,
+                  CheckPolicy check = kCheckSupported) {}
 #endif
 };