Make -Wpessimining-move non-fatal on the tot bots for a bit.

Bug: 1010458
Change-Id: Ie36ee1a87e7801fafdbfc2f38c0762ebbf7cace7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1835155
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701984}

build/config/compiler/BUILD.gn

@@ -1546,6 +1546,12 @@ config("default_warnings") {
           cflags += [
             # TODO(https://crbug.com/1010111): Evaluate and possible enable.
             "-Wno-enum-compare-conditional",
+
+            # TODO(https://crbug.com/1010458): Figure out plan forward,
+            # see bug. Depending on how many instances there are, either
+            # turn off warning when rolling this in, then fix and turn back on,
+            # or fix before the roll.
+            "-Wno-error=pessimizing-move",
           ]
         }
       }