[arm] Fix an accessor return type.

Existing uses are correct but the return type was misleading.

Also clarify some related comments to make the difference between Bits
and BitField more obvious.

BUG=

Review-Url: https://codereview.chromium.org/2275973002
Cr-Commit-Position: refs/heads/master@{#38894}

src/arm/constants-arm.h

@@ -477,40 +477,42 @@ class Instruction {
     *reinterpret_cast<Instr*>(this) = value;
   }
 
-  // Read one particular bit out of the instruction bits.
+  // Extract a single bit from the instruction bits and return it as bit 0 in
+  // the result.
   inline int Bit(int nr) const {
     return (InstructionBits() >> nr) & 1;
   }
 
-  // Read a bit field's value out of the instruction bits.
+  // Extract a bit field <hi:lo> from the instruction bits and return it in the
+  // least-significant bits of the result.
   inline int Bits(int hi, int lo) const {
     return (InstructionBits() >> lo) & ((2 << (hi - lo)) - 1);
   }
 
-  // Read a bit field out of the instruction bits.
+  // Read a bit field <hi:lo>, leaving its position unchanged in the result.
   inline int BitField(int hi, int lo) const {
     return InstructionBits() & (((2 << (hi - lo)) - 1) << lo);
   }
 
   // Static support.
 
-  // Read one particular bit out of the instruction bits.
+  // Extract a single bit from the instruction bits and return it as bit 0 in
+  // the result.
   static inline int Bit(Instr instr, int nr) {
     return (instr >> nr) & 1;
   }
 
-  // Read the value of a bit field out of the instruction bits.
+  // Extract a bit field <hi:lo> from the instruction bits and return it in the
+  // least-significant bits of the result.
   static inline int Bits(Instr instr, int hi, int lo) {
     return (instr >> lo) & ((2 << (hi - lo)) - 1);
   }
 
-
-  // Read a bit field out of the instruction bits.
+  // Read a bit field <hi:lo>, leaving its position unchanged in the result.
   static inline int BitField(Instr instr, int hi, int lo) {
     return instr & (((2 << (hi - lo)) - 1) << lo);
   }
 
-
   // Accessors for the different named fields used in the ARM encoding.
   // The naming of these accessor corresponds to figure A3-1.
   //
@@ -525,13 +527,11 @@ class Instruction {
 
 
   // Generally applicable fields
-  inline Condition ConditionValue() const {
-    return static_cast<Condition>(Bits(31, 28));
-  }
+  inline int ConditionValue() const { return Bits(31, 28); }
   inline Condition ConditionField() const {
     return static_cast<Condition>(BitField(31, 28));
   }
-  DECLARE_STATIC_TYPED_ACCESSOR(Condition, ConditionValue);
+  DECLARE_STATIC_TYPED_ACCESSOR(int, ConditionValue);
   DECLARE_STATIC_TYPED_ACCESSOR(Condition, ConditionField);
 
   inline int TypeValue() const { return Bits(27, 25); }