Modify fileAtPath stat to track if the call was redirected by chrome_elf.

chrome_elf/create_file/chrome_create_file.cc

Index: chrome_elf/create_file/chrome_create_file.cc
diff --git a/chrome_elf/create_file/chrome_create_file.cc b/chrome_elf/create_file/chrome_create_file.cc
index b6744f3f34d38f5f34967bb4c3da44dc50b7e7d9..5fed63e235f01a2b7aa5d712b378bb8059ab02be 100644
--- a/chrome_elf/create_file/chrome_create_file.cc
+++ b/chrome_elf/create_file/chrome_create_file.cc
@@ -11,6 +11,9 @@
 #include "chrome_elf/ntdll_cache.h"
 #include "sandbox/win/src/nt_internals.h"
 
+// Record if the last call to CreateFile was redirected.
+bool g_last_call_was_redirected = false;

[robertshield, 2014/02/18 19:36:03]

I think this should be a monotonically increasing count instead.

[gab, 2014/02/18 19:43:11]

And if you want to go deeper, you could have a periodic task in Chrome looking
for that count to tick and reporting UMA for it.

[robertshield, 2014/02/18 19:46:22]

We could, but we're really interested in seeing this increment across specific
events.

[Cait (Slow), 2014/02/18 23:17:18]

I'll switch it to a count, when we can use to check for specific events, that
way if we ever need a running tally it will only require adding an UMA stat,
chrome-side.

+
 namespace {
 
 // From ShlObj.h in the Windows SDK.
@@ -92,6 +95,7 @@ HANDLE WINAPI CreateFileWRedirect(
     DWORD flags_and_attributes,
     HANDLE template_file) {
   if (ShouldBypass(file_name)) {
+    g_last_call_was_redirected = true;
     return CreateFileNTDLL(file_name,
                            desired_access,
                            share_mode,
@@ -110,6 +114,10 @@ HANDLE WINAPI CreateFileWRedirect(
 
 }
 
+bool LastCallWasRedirected() {
+  return g_last_call_was_redirected;
+}
+
 HANDLE CreateFileNTDLL(
     LPCWSTR file_name,
     DWORD desired_access,