Support the Syzygy instrumenting profiler.

base/debug/profiler.h

Index: base/debug/profiler.h
diff --git a/base/debug/profiler.h b/base/debug/profiler.h
index 69795a507853a83321cf6645ba62e70db71f5ea9..e88d6715b85c11a5cbf746b012136e959d3e33de 100644
--- a/base/debug/profiler.h
+++ b/base/debug/profiler.h
@@ -34,6 +34,26 @@ BASE_EXPORT bool BeingProfiled();
 // Reset profiling after a fork, which disables timers.
 BASE_EXPORT void RestartProfilingAfterFork();
 
+// Returns true iff this executable is instrumented with the Syzygy profiler.
+BASE_EXPORT bool IsBinaryInstrumented();
+
+// A return address resolution function is used to resolve the location
+// on stack where a return address originally resided, to the location where
+// the profiler stashed the original return address.

[jar (doing other things), 2012/02/27 22:44:10]

I couldn't understand this comment.  Specifically, I don't know what it means
to:
"resolve the location on the stack ... to the location where the profiler
stashed the original return address."

I suspect I need more background.  At a minimum, this is a very long sentence,
and a few shorter informative sentences would probably help a lot.

[Sigurður Ásgeirsson, 2012/02/28 16:31:40]

Reworked comment with a lot more detail.

+// This is necessary for V8 and any other code that looks at the return address
+// to see where a call originated and/or rewrites the return address. V8 looks
+// at the return address to identify the JavaScript function that invoked it,
+// and may rewrite return addresses when it garbage collects or optimizes the
+// JIT code.
+typedef uintptr_t (*ReturnAddressLocationResolver)(
+    uintptr_t return_addr_location);
+
+// If this binary is instrumented and the instrumentation supplies a return
+// address resolution function, finds and returns the address resolution
+// function. Otherwise returns NULL.
+BASE_EXPORT ReturnAddressLocationResolver
+    GetProfilerReturnAddrResolutionFunc();
+
 }  // namespace debug
 }  // namespace base