add const to casts

When casting a const value, ensure the cast is const as well.

BUG=webm:1509

Change-Id: I5b597fdcc148d111e9824bc7cf918fc5f24e970f
Reviewed-on: https://chromium-review.googlesource.com/996553Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>

source/compare_common.cc

@@ -55,7 +55,7 @@ uint32_t HammingDistance_C(const uint8_t* src_a,
 
   int i;
   for (i = 0; i < count - 3; i += 4) {
-    uint32_t x = *((uint32_t*)src_a) ^ *((uint32_t*)src_b);  // NOLINT
+    uint32_t x = *((const uint32_t*)src_a) ^ *((const uint32_t*)src_b);
     uint32_t u = x - ((x >> 1) & 0x55555555);
     u = ((u >> 2) & 0x33333333) + (u & 0x33333333);
     diff += ((((u + (u >> 4)) & 0x0f0f0f0f) * 0x01010101) >> 24);

source/convert_from.cc

@@ -1154,8 +1154,8 @@ int I420ToRGB565Dither(const uint8_t* src_y,
     for (y = 0; y < height; ++y) {
       I422ToARGBRow(src_y, src_u, src_v, row_argb, &kYuvI601Constants, width);
       ARGBToRGB565DitherRow(row_argb, dst_rgb565,
-                            *(uint32_t*)(dither4x4 + ((y & 3) << 2)),  // NOLINT
-                            width);                                    // NOLINT
+                            *(const uint32_t*)(dither4x4 + ((y & 3) << 2)),
+                            width);
       dst_rgb565 += dst_stride_rgb565;
       src_y += src_stride_y;
       if (y & 1) {

source/convert_from_argb.cc

@@ -1050,8 +1050,8 @@ int ARGBToRGB565Dither(const uint8_t* src_argb,
 
   for (y = 0; y < height; ++y) {
     ARGBToRGB565DitherRow(src_argb, dst_rgb565,
-                          *(uint32_t*)(dither4x4 + ((y & 3) << 2)),  // NOLINT
-                          width); /* NOLINT */
+                          *(const uint32_t*)(dither4x4 + ((y & 3) << 2)),
+                          width);
     src_argb += src_stride_argb;
     dst_rgb565 += dst_stride_rgb565;
   }