Refactor rangelist handling to prepare for dwarf5 .debug_rngslist

Dwarf5 introduces a new .debug_rngslist section, to take the place
of the Dwarf4 .debug_ranges. However, the dwarf version is CU-based,
and not file-based, so there can be both sections, and which section
the CU needs isn't known until the dwarf parser encounters either
DW_AT_ranges (dwarf 4 and lower) or DW_AT_rnglists_base (dwarf 5).

This change refactors the code around range lists and range list
readers to defer the decision of what section to parse until
the relevant attribute is found. It moves the range list section
reader from the range-list handler itself (which doesn't know which
section it will use) to the CU context, and then lets the handler
know when it encounters DW_AT_ranges.

I will add a reader for the new dwarf5 section, along with the code to
interpret the new section, and its forms and such in a subsequent patch.

Change-Id: Ie92e4c9daa3f0acb98d7ef74f6b9c2065db849b1
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/2433684
Reviewed-by: Mark Mentovai <mark@chromium.org>

src/common/dwarf/dwarf2reader.cc

@@ -1569,10 +1569,11 @@ void LineInfo::ReadLines() {
 }
 
 RangeListReader::RangeListReader(const uint8_t* buffer, uint64_t size,
-                                 ByteReader* reader, RangeListHandler* handler)
-    : buffer_(buffer), size_(size), reader_(reader), handler_(handler) { }
+                                 ByteReader* reader)
+    : buffer_(buffer), size_(size), reader_(reader) { }
 
-bool RangeListReader::ReadRangeList(uint64_t offset) {
+bool RangeListReader::ReadRangeList(uint64_t offset,
+                                    RangeListHandler* handler) {
   const uint64_t max_address =
     (reader_->AddressSize() == 4) ? 0xffffffffUL
                                   : 0xffffffffffffffffULL;
@@ -1589,12 +1590,12 @@ bool RangeListReader::ReadRangeList(uint64_t offset) {
       reader_->ReadAddress(buffer_ + offset + reader_->AddressSize());
 
     if (start_address == max_address) { // Base address selection
-      handler_->SetBaseAddress(end_address);
+      handler->SetBaseAddress(end_address);
     } else if (start_address == 0 && end_address == 0) { // End-of-list
-      handler_->Finish();
+      handler->Finish();
       list_end = true;
     } else { // Add a range entry
-      handler_->AddRange(start_address, end_address);
+      handler->AddRange(start_address, end_address);
     }
 
     offset += entry_size;

src/common/dwarf/dwarf2reader.h

@@ -243,16 +243,14 @@ class RangeListHandler {
 
 class RangeListReader {
  public:
-  RangeListReader(const uint8_t* buffer, uint64_t size, ByteReader* reader,
-                  RangeListHandler* handler);
+  RangeListReader(const uint8_t* buffer, uint64_t size, ByteReader* reader);
 
-  bool ReadRangeList(uint64_t offset);
+  bool ReadRangeList(uint64_t offset, RangeListHandler* handler);
 
  private:
   const uint8_t* buffer_;
   uint64_t size_;
   ByteReader* reader_;
-  RangeListHandler* handler_;
 };
 
 // This class is the main interface between the reader and the