Don't include map name if the consumer doesn't want names.

Simpleperf doesn't need the name, so avoid the string copies.

This seems to speed up simpleperf by around 20%.

Test: backtrace_test libunwindstack_test
Change-Id: Iba064c7078f7e5ecfc9d8539ba09c14495a52158
diff --git a/libunwindstack/Unwinder.cpp b/libunwindstack/Unwinder.cpp
index 94edb1c..27262bd 100644
--- a/libunwindstack/Unwinder.cpp
+++ b/libunwindstack/Unwinder.cpp
@@ -61,7 +61,9 @@
     frame->map_offset = info->offset;
     frame->map_load_bias = info->load_bias;
     frame->map_flags = info->flags;
-    frame->map_name = info->name;
+    if (resolve_names_) {
+      frame->map_name = info->name;
+    }
     frame->rel_pc = dex_pc - info->start;
   } else {
     frame->rel_pc = dex_pc;
@@ -96,7 +98,9 @@
     return;
   }
 
-  frame->map_name = map_info->name;
+  if (resolve_names_) {
+    frame->map_name = map_info->name;
+  }
   frame->map_offset = map_info->offset;
   frame->map_start = map_info->start;
   frame->map_end = map_info->end;
diff --git a/libunwindstack/tests/UnwinderTest.cpp b/libunwindstack/tests/UnwinderTest.cpp
index e44b225..551f46c 100644
--- a/libunwindstack/tests/UnwinderTest.cpp
+++ b/libunwindstack/tests/UnwinderTest.cpp
@@ -221,7 +221,7 @@
   EXPECT_EQ(0x10000U, frame->sp);
   EXPECT_EQ("", frame->function_name);
   EXPECT_EQ(0U, frame->function_offset);
-  EXPECT_EQ("/system/fake/libc.so", frame->map_name);
+  EXPECT_EQ("", frame->map_name);
   EXPECT_EQ(0U, frame->map_offset);
   EXPECT_EQ(0x1000U, frame->map_start);
   EXPECT_EQ(0x8000U, frame->map_end);
@@ -235,7 +235,7 @@
   EXPECT_EQ(0x10010U, frame->sp);
   EXPECT_EQ("", frame->function_name);
   EXPECT_EQ(0U, frame->function_offset);
-  EXPECT_EQ("/system/fake/libc.so", frame->map_name);
+  EXPECT_EQ("", frame->map_name);
   EXPECT_EQ(0U, frame->map_offset);
   EXPECT_EQ(0x1000U, frame->map_start);
   EXPECT_EQ(0x8000U, frame->map_end);
@@ -249,7 +249,7 @@
   EXPECT_EQ(0x10020U, frame->sp);
   EXPECT_EQ("", frame->function_name);
   EXPECT_EQ(0U, frame->function_offset);
-  EXPECT_EQ("/system/fake/libc.so", frame->map_name);
+  EXPECT_EQ("", frame->map_name);
   EXPECT_EQ(0U, frame->map_offset);
   EXPECT_EQ(0x1000U, frame->map_start);
   EXPECT_EQ(0x8000U, frame->map_end);