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

This reverts commit 11ec6a9b.

Reason for revert: The failed screenshot tests were not caused by this change

Original change's description:
> 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/+/1909669
> Reviewed-by: Keishi Hattori <keishi@chromium.org>
> Commit-Queue: Keishi Hattori <keishi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#714159}

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

Change-Id: Ifff4b8df577ad13e2cbffcfe90044caac9b0a888
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1021236
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1909654Reviewed-by: Eric Roman <eroman@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Auto-Submit: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714282}

extensions/common/image_util.cc

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