[sanitizer_common][Fuchsia] Update Fuchsia sanitizer markup

[mcgrathr]

Summary

Include URLs to the markup format specification in code comments.
Use sanitizer markup in the sancov message about a dump just produced.

[phosek]

LGTM

lib/sanitizer_common/sanitizer_coverage_fuchsia.cc

if (array_) {
       CHECK_NE(vmo_, MX_HANDLE_INVALID);
 
       // Publish the VMO to the system, where it can be collected and
       // analyzed after this process exits.  This always consumes the VMO
       // handle.  Any failure is just logged and not indicated to us.
       __sanitizer_publish_data(kSancovSinkName, vmo_);
       vmo_ = MX_HANDLE_INVALID;
 
-      // This will route to __sanitizer_log_write, which will ensure
-      // that information about shared libraries is written out.
-      Printf("SanitizerCoverage: published '%s' with up to %u PCs\n", vmo_name_,
-             next_index_ - 1);
+      // This will route to __sanitizer_log_write, which will ensure that
+      // information about shared libraries is written out.  This message
+      // uses the `dumpfile` symbolizer markup element to highlight the
+      // dump.  See the explanation for this in:
+      // https://fuchsia.googlesource.com/magenta/+/master/docs/symbolizer_markup.md
+      Printf("SanitizerCoverage: {{{dumpfile:%s:%s}}} with up to %u PCs\n",
+             kSancovSinkName, vmo_name_, next_index_ - 1);
     }
   }
 
  private:
   // We map in the largest possible view into the VMO: one word
   // for every possible 32-bit index value.  This avoids the need
   // to change the mapping when increasing the size of the VMO.
   // We can always spare the 32G of address space.

lib/sanitizer_common/sanitizer_symbolizer_fuchsia.cc

 
 namespace __sanitizer {
 
 // For Fuchsia we don't do any actual symbolization per se.
 // Instead, we emit text containing raw addresses and raw linkage
 // symbol names, embedded in Fuchsia's symbolization markup format.
 // Fuchsia's logging infrastructure emits enough information about
 // process memory layout that a post-processing filter can do the
-// symbolization and pretty-print the markup.
-// TODO(mcgrathr): URL to markup format document
+// symbolization and pretty-print the markup.  See the spec at:
+// https://fuchsia.googlesource.com/magenta/+/master/docs/symbolizer_markup.md
 
 // This is used by UBSan for type names, and by ASan for global variable names.
 constexpr const char *kFormatDemangle = "{{{symbol:%s}}}";
 constexpr uptr kFormatDemangleMax = 1024;  // Arbitrary.
 
 // Function name or equivalent from PC location.
 constexpr const char *kFormatFunction = "{{{pc:%p}}}";
 constexpr uptr kFormatFunctionMax = 64; // More than big enough for 64-bit hex.