Fix the TSan suppression for issue 794920

TSan suppressions can't be applied to memory allocation stacks in
the reports, only to memory access stacks.
Therefore suppress the access that occurs in base::debug::SetCrashKeyString()

BUG=794920
TBR=rsesek@chromium.org

Change-Id: I607bf4f13af69eade9a5c745d556a615f4c2d1c2
Reviewed-on: https://chromium-review.googlesource.com/972984Reviewed-by: Alexander Potapenko <glider@chromium.org>
Commit-Queue: Alexander Potapenko <glider@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544724}

build/sanitizers/tsan_suppressions.cc

@@ -256,7 +256,7 @@ char kTSanDefaultSuppressions[] =
     "race:base::i18n::SetICUDefaultLocale\n"
 
     // https://crbug.com/794920
-    "race:crash_reporter::InitializeCrashKeys\n"
+    "race:base::debug::SetCrashKeyString\n"
 
     // http://crbug.com/795110
     "race:third_party/fontconfig/*\n"