win vs2015: avoid some variable shadowing warnings in crypto/p224

e.g.

d:\src\cr2\src\crypto\p224.cc(478): error C2220: warning treated as error - no 'object' file generated
d:\src\cr2\src\crypto\p224.cc(478): warning C4456: declaration of 'j' hides previous local declaration
d:\src\cr2\src\crypto\p224.cc(447): note: see declaration of 'j'
d:\src\cr2\src\crypto\p224.cc(498): warning C4456: declaration of 'i' hides previous local declaration
d:\src\cr2\src\crypto\p224.cc(447): note: see declaration of 'i'
d:\src\cr2\src\crypto\p224.cc(516): warning C4456: declaration of 'i' hides previous local declaration
d:\src\cr2\src\crypto\p224.cc(447): note: see declaration of 'i'
d:\src\cr2\src\crypto\p224.cc(526): warning C4456: declaration of 'i' hides previous local declaration
d:\src\cr2\src\crypto\p224.cc(447): note: see declaration of 'i'
d:\src\cr2\src\crypto\p224.cc(694): warning C4458: declaration of 'x' hides class member
d:\src\cr2\src\crypto\p224.h(35): note: see declaration of 'crypto::p224::Point::x'
d:\src\cr2\src\crypto\p224.cc(694): warning C4458: declaration of 'y' hides class member
d:\src\cr2\src\crypto\p224.h(35): note: see declaration of 'crypto::p224::Point::y'

R=rsleevi@chromium.org
BUG=440500

Review URL: https://codereview.chromium.org/945633003

Cr-Commit-Position: refs/heads/master@{#317398}

crypto/p224.cc

@@ -475,8 +475,8 @@ void AddJacobian(Point *out,
   uint32 x_equal = IsZero(h);
 
   // I = (2*H)²
-  for (int j = 0; j < 8; j++) {
-    i[j] = h[j] << 1;
+  for (int k = 0; k < 8; k++) {
+    i[k] = h[k] << 1;
   }
   Reduce(&i);
   Square(&i, i);
@@ -495,8 +495,8 @@ void AddJacobian(Point *out,
     return;
   }
 
-  for (int i = 0; i < 8; i++) {
-    r[i] <<= 1;
+  for (int k = 0; k < 8; k++) {
+    r[k] <<= 1;
   }
   Reduce(&r);
 
@@ -513,8 +513,8 @@ void AddJacobian(Point *out,
   Mul(&out->z, out->z, h);
 
   // X3 = r²-J-2*V
-  for (int i = 0; i < 8; i++) {
-    z1z1[i] = v[i] << 1;
+  for (int k = 0; k < 8; k++) {
+    z1z1[k] = v[k] << 1;
   }
   Add(&z1z1, j, z1z1);
   Reduce(&z1z1);
@@ -523,8 +523,8 @@ void AddJacobian(Point *out,
   Reduce(&out->x);
 
   // Y3 = r*(V-X3)-2*S1*J
-  for (int i = 0; i < 8; i++) {
-    s1[i] <<= 1;
+  for (int k = 0; k < 8; k++) {
+    s1[k] <<= 1;
   }
   Mul(&s1, s1, j);
   Subtract(&z1z1, v, out->x);
@@ -691,7 +691,7 @@ bool Point::SetFromString(const base::StringPiece& in) {
 }
 
 std::string Point::ToString() const {
-  FieldElement zinv, zinv_sq, x, y;
+  FieldElement zinv, zinv_sq, xx, yy;
 
   // If this is the point at infinity we return a string of all zeros.
   if (IsZero(this->z)) {
@@ -701,16 +701,16 @@ std::string Point::ToString() const {
 
   Invert(&zinv, this->z);
   Square(&zinv_sq, zinv);
-  Mul(&x, this->x, zinv_sq);
+  Mul(&xx, x, zinv_sq);
   Mul(&zinv_sq, zinv_sq, zinv);
-  Mul(&y, this->y, zinv_sq);
+  Mul(&yy, y, zinv_sq);
 
-  Contract(&x);
-  Contract(&y);
+  Contract(&xx);
+  Contract(&yy);
 
   uint32 outwords[14];
-  Put224Bits(outwords, x);
-  Put224Bits(outwords + 7, y);
+  Put224Bits(outwords, xx);
+  Put224Bits(outwords + 7, yy);
   return std::string(reinterpret_cast<const char*>(outwords), sizeof(outwords));
 }