Chrome Version: tip
OS: Linux x86-64

What steps will reproduce the problem?
(1) Build content_browsertests with LTO:

$ gn gen out/lto '--args=is_debug=false is_cfi=false use_thin_lto=false allow_posix_link_time_opt=true symbol_level=1 use_goma=true' --check
$ ninja -C out/lto content_browsertests

(2) Run the test case:

$ ./out/lto/content_browsertests --gtest_filter=IFrameZoomBrowserTest.RedirectToPageWithSubframeZoomsCorrectly

(3) Observe the test failure:

IFrameZoomBrowserTest.RedirectToPageWithSubframeZoomsCorrectly (run #1):
[ RUN      ] IFrameZoomBrowserTest.RedirectToPageWithSubframeZoomsCorrectly
[20328:20328:0316/084729.052130:4912313902:WARNING:audio_manager.cc(295)] Multiple instances of AudioManager detected
[20328:20328:0316/084729.052199:4912313948:WARNING:audio_manager.cc(254)] Multiple instances of AudioManager detected
Xlib:  extension "RANDR" missing on display ":9".
../../content/browser/zoom_browsertest.cc:590: Failure
The difference between kZoomFactorForRedirectedHost and GetMainFrameZoomFactor(web_contents(), main_frame_window_border) is 0.0065666041275798115, which exceeds 0.001, where
kZoomFactorForRedirectedHost evaluates to 1.5,
GetMainFrameZoomFactor(web_contents(), main_frame_window_border) evaluates to 1.4934333958724202, and
0.001 evaluates to 0.001.
[  FAILED  ] IFrameZoomBrowserTest.RedirectToPageWithSubframeZoomsCorrectly, where TypeParam =  and GetParam() =  (296 ms)

This is observed on a number of bots:
https://build.chromium.org/p/chromium.fyi/builders/CFI%20Linux/builds/7663
https://build.chromium.org/p/chromium.fyi/builders/CFI%20Linux%20Full/builds/1603
https://build.chromium.org/p/chromium.fyi/builders/LTO%20Linux/builds/2181
https://build.chromium.org/p/chromium.fyi/builders/ThinLTO%20Linux%20ToT/builds/1308
https://build.chromium.org/p/chromium.fyi/builders/CFI%20Linux%20ToT/builds/5834

It could be that some other bots / configurations are affected. I don't know an easy way to check that.

Also, it seems that the test almost pass. It's either a loss of precision (somehow) or some bad timing.

Settings as P1 as it's the cause of multiple bots being red.