[vm/compiler] Strip org-dartlang-sdk URI prefix to resolve DWARF paths.

Before, we only stripped `org-dartlang-sdk:///` as a prefix when it was
followed by `sdk/...`, which happens for code compiled with the Dart
SDK. However, the same prefix can show up in Flutter code (e.g.,
`org-dartlang-sdk:///third_party/dart/sdk/...`).  Thus, except for one
case, just strip the prefix at all times when `--resolve-dwarf-paths`
is set, leaving a relative path.

The one case is `org-dartlang-sdk:///flutter/`, which appears in the
resolved version of `dart:ui` (`org-dartlang-sdk:///flutter/lib/ui`),
where the `flutter` isn't part of the actual filesystem path. In this
case, we strip off the `flutter/` as well.

TEST=vm/dart{,_2}/use_resolve_dwarf_paths_flag

Bug: #44325
Change-Id: Ia9abca877e41657089a438d4723ff08a2e16fe69
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-dwarf-linux-product-x64-try,vm-kernel-precomp-linux-release-x64-try,vm-kernel-precomp-nnbd-mac-release-arm64-try,vm-kernel-precomp-nnbd-win-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/268762
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>

runtime/vm/dwarf.cc

@@ -814,7 +814,10 @@ void Dwarf::WriteLineNumberProgramFromCodeSourceMaps(
 
 static constexpr char kResolvedFileRoot[] = "file:///";
 static constexpr intptr_t kResolvedFileRootLen = sizeof(kResolvedFileRoot) - 1;
-static constexpr char kResolvedSdkRoot[] = "org-dartlang-sdk:///sdk/";
+static constexpr char kResolvedFlutterRoot[] = "org-dartlang-sdk:///flutter/";
+static constexpr intptr_t kResolvedFlutterRootLen =
+    sizeof(kResolvedFlutterRoot) - 1;
+static constexpr char kResolvedSdkRoot[] = "org-dartlang-sdk:///";
 static constexpr intptr_t kResolvedSdkRootLen = sizeof(kResolvedSdkRoot) - 1;
 static constexpr char kResolvedGoogle3Root[] = "google3:///";
 static constexpr intptr_t kResolvedGoogle3RootLen =
@@ -830,10 +833,15 @@ static const char* ConvertResolvedURI(const char* str) {
     return str + kResolvedFileRootLen - 1;  // Leave a '/' on the front.
 #endif
   }
+  // Must do kResolvedFlutterRoot before kResolvedSdkRoot, since the latter is
+  // a prefix of the former.
+  if (len > kResolvedFlutterRootLen &&
+      strncmp(str, kResolvedFlutterRoot, kResolvedFlutterRootLen) == 0) {
+    return str + kResolvedFlutterRootLen;  // Strip off the entire prefix.
+  }
   if (len > kResolvedSdkRootLen &&
       strncmp(str, kResolvedSdkRoot, kResolvedSdkRootLen) == 0) {
-    // Leave "sdk/" as a prefix in the returned path.
-    return str + (kResolvedSdkRootLen - 4);
+    return str + kResolvedSdkRootLen;  // Strip off the entire prefix.
   }
   if (len > kResolvedGoogle3RootLen &&
       strncmp(str, kResolvedGoogle3Root, kResolvedGoogle3RootLen) == 0) {