Do not read /proc/self/exe before forking if Chrome is ran under Valgrind.

This should prevent ui_tests from crashing under Valgrind on Linux.
This fix was suggested by kcc (see the discussion of issue 28439)

BUG=28439

Review URL: http://codereview.chromium.org/6331002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71590 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/child_process_host.cc

@@ -7,6 +7,7 @@
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/path_service.h"
+#include "base/third_party/dynamic_annotations/dynamic_annotations.h"
 #include "chrome/common/child_process_info.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths_internal.h"
@@ -56,7 +57,10 @@ FilePath ChildProcessHost::GetChildPath(bool allow_self) {
 #if defined(OS_LINUX)
   // Use /proc/self/exe rather than our known binary path so updates
   // can't swap out the binary from underneath us.
-  if (allow_self)
+  // When running under Valgrind, forking /proc/self/exe ends up forking the
+  // Valgrind executable, which then crashes. However, it's almost safe to
+  // assume that the updates won't happen while testing with Valgrind tools.
+  if (allow_self && !RunningOnValgrind())
     return FilePath("/proc/self/exe");
 #endif