Stack sampling profiler: fix off-by-one error on truncated stacks

Stacks that are truncated due to the Win32StackFrameUnwinder being
unable to unwind are being reported with an extra frame.

BUG=555770

Review URL: https://codereview.chromium.org/1469983002

Cr-Commit-Position: refs/heads/master@{#361230}

base/profiler/native_stack_sampler_win.cc

@@ -148,7 +148,7 @@ int RecordStack(CONTEXT* context, int max_stack_size,
   for (; (i < max_stack_size) && context->Rip; ++i) {
     instruction_pointers[i] = reinterpret_cast<const void*>(context->Rip);
     if (!frame_unwinder.TryUnwind(context, &modules[i]))
-      return i + 1;
+      return i;
   }
   return i;
 #else

base/profiler/stack_sampling_profiler_unittest.cc

@@ -515,15 +515,14 @@ void TestLibraryUnload(bool wait_until_unloaded) {
       << FormatSampleForDiagnosticOutput(sample, profile.modules);
 
   if (wait_until_unloaded) {
-    // The stack should look like this, resulting in two frames between
-    // SignalAndWaitUntilSignaled and the last frame, which should be the one in
-    // the now-unloaded library:
+    // The stack should look like this, resulting one frame after
+    // SignalAndWaitUntilSignaled. The frame in the now-unloaded library is not
+    // recorded since we can't get module information.
     //
     // ... WaitableEvent and system frames ...
     // TargetThread::SignalAndWaitUntilSignaled
     // TargetThread::OtherLibraryCallback
-    // InvokeCallbackFunction (in other library, now unloaded)
-    EXPECT_EQ(2, (sample.end() - 1) - end_frame)
+    EXPECT_EQ(2, sample.end() - end_frame)
         << "Stack:\n"
         << FormatSampleForDiagnosticOutput(sample, profile.modules);
   } else {