StackTraceDeobfuscator should never provide null methodName (#9997)

Improves accuracy of deobfuscated stack traces by using the best answer
between original JS names, symbol maps, and source maps, by both
avoiding taking an identifier from the sourcemap if none is provided,
and normalizing away chromium specific prefixes in stack trace elements.

Fixes #9996
Follow-up #9936

Author: niloc132

user/src/com/google/gwt/core/server/StackTraceDeobfuscator.java

@@ -26,6 +26,7 @@
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.net.URL;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -186,9 +187,9 @@ public final StackTraceElement[] resymbolize(StackTraceElement[] st, String stro
       return null;
     }
     // Warm the symbol cache for all symbols in this stack trace.
-    Set<String> requiredSymbols = new HashSet<String>();
+    Set<String> requiredSymbols = new HashSet<>();
     for (StackTraceElement ste : st) {
-      requiredSymbols.add(ste.getMethodName());
+      requiredSymbols.add(normalizeSymbol(ste.getMethodName()));
     }
     loadSymbolMap(strongName, requiredSymbols);
 
@@ -199,6 +200,17 @@ public final StackTraceElement[] resymbolize(StackTraceElement[] st, String stro
     return newSt;
   }
 
+  /**
+   * Helper to clean up client-provided symbols.
+   */
+  private static String normalizeSymbol(String symbol) {
+    // Chrome prefixes "new " for constructor calls, eliminate the prefix
+    if (symbol.startsWith("new ")) {
+      symbol = symbol.substring(4);
+    }
+    return symbol;
+  }
+
   /**
    * Best effort resymbolization of a single stack trace element.
    *
@@ -305,7 +317,13 @@ public final StackTraceElement resymbolize(StackTraceElement ste, String strongN
 
           if (declaringClass == null || declaringClass.equals(ste.getClassName())) {
             declaringClass = mappingForLine.getOriginalFile();
-            methodName = mappingForLine.getIdentifier().orElse(null);
+            if (mappingForLine.getIdentifier().isPresent()) {
+              // Only overwrite the name if the sourcemap had an explicit identifier
+              methodName = mappingForLine.getIdentifier().get();
+            } else if (methodName == null) {
+              // No other name was provided by symbolMaps, fall back to JS name
+              methodName = ste.getMethodName();
+            }
           }
           fileName = mappingForLine.getOriginalFile();
           lineNumber = mappingForLine.getLineNumber();
@@ -366,9 +384,8 @@ private String loadStreamAsString(InputStream stream) {
   }
 
   private String loadOneSymbol(String strongName, String symbol) {
-    Set<String> symbolSet = new HashSet<String>();
-    symbolSet.add(symbol);
-    Map<String, String> symbolMap = loadSymbolMap(strongName, symbolSet);
+    symbol = normalizeSymbol(symbol);
+    Map<String, String> symbolMap = loadSymbolMap(strongName, Collections.singleton(symbol));
     return symbolMap.get(symbol);
   }