Revert "Make use of new hex decoding function for extensions color string parser."

This reverts commit 2de0ccb8.

Reason for revert: Suspecting cause for screenshot test failure. Seems unlikely but this is the only color related CL in regression range. crbug.com/1023255

Original change's description:
> Make use of new hex decoding function for extensions color string parser.
> 
> Bug: 1021236
> Change-Id: I1d1b5180048eb36fa78406a02fc3277cba0dcf63
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1904809
> Commit-Queue: Eric Roman <eroman@chromium.org>
> Commit-Queue: Reilly Grant <reillyg@chromium.org>
> Auto-Submit: Eric Roman <eroman@chromium.org>
> Reviewed-by: Reilly Grant <reillyg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#713942}

TBR=eroman@chromium.org,reillyg@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1021236
Change-Id: I474f4e07583f571722e4bacf28ae482c071276a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1909669Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714159}

extensions/common/image_util.cc

@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include <algorithm>
+#include <vector>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ -64,9 +65,9 @@ bool ParseHexColorString(const std::string& color_string, SkColor* result) {
       formatted_color += color_string[i];
     }
   } else if (color_string.length() == 7) {
-    formatted_color.assign(color_string, 1, 6);
+    formatted_color = color_string.substr(1, 6);
   } else if (color_string.length() == 9) {
-    formatted_color.assign(color_string, 1, 8);
+    formatted_color = color_string.substr(1, 8);
   } else {
     return false;
   }
@@ -76,9 +77,10 @@ bool ParseHexColorString(const std::string& color_string, SkColor* result) {
     formatted_color += "FF";
   }
 
-  // Convert the hex string to an integer.
-  std::array<uint8_t, 4> color_bytes;
-  if (!base::HexStringToSpan(formatted_color, color_bytes))
+  // Convert the string to an integer and make sure it is in the correct value
+  // range.
+  std::vector<uint8_t> color_bytes;
+  if (!base::HexStringToBytes(formatted_color, &color_bytes))
     return false;
 
   *result = SkColorSetARGB(color_bytes[3], color_bytes[0], color_bytes[1],