NPE in StackTraceDeobfuscator for missing identifiers, plus incorrect methodNames from chromium

[niloc132]

GWT version: HEAD-SNAPSHOT
Browser (with version): any/chrome
Operating System: any

This issue is discussing two related issues, one a regression in GWT since #9936 and the other a regression in the past few years in chromium.

• The GWT regression is mentioned at StackTraceDeobfuscator sometimes produces total nonsense #9931 (comment):

  So if the outer if is entered, there is a possibility that

   methodName = mappingForLine.getIdentifier().orElse(null);
  

  sets methodName to null.

  This results in an NPE while creating the replacement StackTraceElement, preventing reading the exception.

• The Chromium issue is that when building a stack element of the form at method (file:row:col), the method name now may have a new prefix. This is not found in the symbol map file, so cannot be deobfuscated (though sourcemaps can try to take the row/col and figure out which file it should have come from). Example JS stack trace (with -style PRETTY):

  java.lang.RuntimeException: Runtime Exception
      at RuntimeException_0.createError (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:912:10)
      at RuntimeException_0.initializeBackingError (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:946:40)
      at RuntimeException_0.Throwable_0 (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:877:8)
      at RuntimeException_0.Exception_0 (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:961:15)
      at new RuntimeException_0 (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:970:15)
      at $throwException (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:4315:14)
      at LoggingRPCTest.testStackMapDeobfuscation (com.google.gwt.user.LoggingRPCSuite.JUnit-0.js:4369:5)
  

  Instead of new RuntimeException_0, our symbol maps expect RuntimeException_0, so this prefix needs to be removed.