[Fuchsia] For profiling, export symbols, profile the VM (#3756)

content_handler/BUILD.gn

@@ -96,6 +96,16 @@ template("flutter_content_handler") {
         "//magma:vulkan",
       ]
     }
+
+    # The flags below are needed so that Dart's CPU profiler can walk the
+    # C++ stack.
+    cflags = [
+      "-mno-omit-leaf-frame-pointer",
+      "-fno-omit-frame-pointer",
+    ]
+    # This flag is needed so that the call to dladdr() in Dart's native symbol
+    # resolver can report good symbol information for the CPU profiler.
+    ldflags = [ "-rdynamic" ]
   }
 }
 

runtime/dart_init.cc

@@ -391,7 +391,10 @@ static std::vector<const char*> ProfilingFlags(bool enable_profiling) {
         // Raspberry Pi devices but quite low for current smartphones.
         "--profile_period=1000",
         // This is the default. But just be explicit.
-        "--profiler"};
+        "--profiler",
+        // This instructs the profiler to walk C++ frames, and to include
+        // them in the profile.
+        "--profile-vm"};
   } else {
     return {"--no-profiler"};
   }