trace_processor: add code for parsing a trace

This CL utilises the previously introduced ProtoDecoder class to parse a
Trace into its important components. It doesn't do anything with the
parsed data yet but it lays the skeleton for writing to TraceStorage in
a subsequent CL.

Bug: 80416541
Change-Id: Id0422968adea16a98ec46b583057e440cd5274cf
diff --git a/src/protozero/proto_decoder_unittest.cc b/src/protozero/proto_decoder_unittest.cc
index fff9dba..a3b5b69 100644
--- a/src/protozero/proto_decoder_unittest.cc
+++ b/src/protozero/proto_decoder_unittest.cc
@@ -49,9 +49,9 @@
 
   ASSERT_EQ(field.id, 1);
   ASSERT_EQ(field.type, proto_utils::FieldType::kFieldTypeLengthDelimited);
-  ASSERT_EQ(field.length_value.length, sizeof(kTestString) - 1);
+  ASSERT_EQ(field.length_limited.length, sizeof(kTestString) - 1);
   for (size_t i = 0; i < sizeof(kTestString) - 1; i++) {
-    ASSERT_EQ(field.length_value.data[i], kTestString[i]);
+    ASSERT_EQ(field.length_limited.data[i], kTestString[i]);
   }
 }
 
@@ -93,7 +93,7 @@
     ASSERT_EQ(exp.type, field.type);
 
     if (field.type == kFieldTypeLengthDelimited) {
-      ASSERT_EQ(exp.int_value, field.length_value.length);
+      ASSERT_EQ(exp.int_value, field.length_limited.length);
     } else {
       ASSERT_EQ(exp.int_value, field.int_value);
     }