base: Symbolize stace traces on official builds if unwind tables are present.

This will allow tests built with is_official_build=true to produce symbolized
stack traces during failures by explicitly setting exclude_unwind_tables
to false. This will be used by the chrome-branded + is_official testers that
have been spun up on https://ci.chromium.org/p/chrome/g/chrome/console

Note that any official build that doesn't touch exclude_unwind_tables will still
have unsymbolized stack traces since exclude_unwind_tables defaults to true
for official builds:
https://source.chromium.org/chromium/chromium/src/+/master:build/config/compiler/compiler.gni;l=96

Consequently, every other official builder will still have this symbolizing
code excluded from the build products.

Bug: 1041069
Change-Id: I937dbe01c38a29b1aff01d471807a9a492109645
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2001749Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732830}

base/debug/stack_trace_posix.cc

@@ -531,7 +531,7 @@ class SandboxSymbolizeHelper {
   int GetFileDescriptor(const char* file_path) {
     int fd = -1;
 
-#if !defined(OFFICIAL_BUILD)
+#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
     if (file_path) {
       // The assumption here is that iterating over std::map<std::string, int>
       // using a const_iterator does not allocate dynamic memory, hense it is
@@ -552,7 +552,7 @@ class SandboxSymbolizeHelper {
         fd = -1;
       }
     }
-#endif  // !defined(OFFICIAL_BUILD)
+#endif  // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
 
     return fd;
   }
@@ -681,7 +681,7 @@ class SandboxSymbolizeHelper {
     // Pre-opening and caching the file descriptors of all loaded modules is
     // not safe for production builds.  Hence it is only done in non-official
     // builds.  For more details, take a look at: http://crbug.com/341966.
-#if !defined(OFFICIAL_BUILD)
+#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
     // Open the object files for all read-only executable regions and cache
     // their file descriptors.
     std::vector<MappedMemoryRegion>::const_iterator it;
@@ -718,7 +718,7 @@ class SandboxSymbolizeHelper {
         }
       }
     }
-#endif  // !defined(OFFICIAL_BUILD)
+#endif  // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
   }
 
   // Initializes and installs the symbolization callback.
@@ -740,7 +740,7 @@ class SandboxSymbolizeHelper {
 
   // Closes all file descriptors owned by this instance.
   void CloseObjectFiles() {
-#if !defined(OFFICIAL_BUILD)
+#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
     std::map<std::string, int>::iterator it;
     for (it = modules_.begin(); it != modules_.end(); ++it) {
       int ret = IGNORE_EINTR(close(it->second));
@@ -748,18 +748,18 @@ class SandboxSymbolizeHelper {
       it->second = -1;
     }
     modules_.clear();
-#endif  // !defined(OFFICIAL_BUILD)
+#endif  // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
   }
 
   // Set to true upon successful initialization.
   bool is_initialized_;
 
-#if !defined(OFFICIAL_BUILD)
+#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
   // Mapping from file name to file descriptor.  Includes file descriptors
   // for all successfully opened object files and the file descriptor for
   // /proc/self/maps.  This code is not safe for production builds.
   std::map<std::string, int> modules_;
-#endif  // !defined(OFFICIAL_BUILD)
+#endif  // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
 
   // Cache for the process memory regions.  Produced by parsing the contents
   // of /proc/self/maps cache.