Fix mime parsing to require slash in mime

When migrating ParseContentType() from http_util to become
ParseMimeType() I noticed that code to check for a slash in the mime
type was inadvertently looking through the entire string.

Bug: 1202034
Change-Id: If78c75be6e302f6cc2314264bd68ec4090b81732
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2896198
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#883248}

net/base/mime_util.cc

@@ -466,11 +466,8 @@ bool ParseMimeType(const std::string& type_str,
     type_end = type_str.length();
 
   // Reject a mime-type if it does not include a slash.
-  // TODO(crbug.com/1202034): This is currently matching old code to search
-  // anywhere in the string for a slash. Update to require the slash in the
-  // mime which was the intention.
   size_t slash_pos = type_str.find_first_of('/');
-  if (slash_pos == std::string::npos)
+  if (slash_pos == std::string::npos || slash_pos > type_end)
     return false;
   if (mime_type)
     *mime_type = type_str.substr(type_val, type_end - type_val);

net/base/mime_util_unittest.cc

@@ -244,8 +244,6 @@ TEST(MimeUtilTest, TestParseMimeType) {
       {"/ts", "/ts", {}},
       {"/s", "/s", {}},
       {"/", "/", {}},
-      // TODO(crbug.com/1202034): This is a bug and should fail.
-      {"t / s", "t", {}},
   };
   for (const auto& test : tests) {
     std::string mime_type;
@@ -258,6 +256,7 @@ TEST(MimeUtilTest, TestParseMimeType) {
            // Must have slash in mime type.
            "",
            "ts",
+           "t / s",
        }) {
     EXPECT_FALSE(ParseMimeType(type_str, nullptr, nullptr));
   }