perf(cdk/a11y): only check for high contrast mode once #22561
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I noticed this in the profiler while working on angular/material.angular.io#961. The `_applyBodyHighContrastModeCssClasses` method is called in the constructor of the `A11yModule` and `MatCommonModule` which means that it'll be invoked whenever a new root injector is created for a module importing any Material module (e.g. lazy-loaded route or dynamically-created component). Since it calls into `getHighContrastMode` and it touches the class list of `document.body`, it has the potential of causing some some slow layouts. This can be observed either when switching pages in the dev app or by profiling the example creation on material.angular.io. These changes resolve the issue by ensuring that we only run the logic once.
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I noticed this in the profiler while working on angular/material.angular.io#961. The `_applyBodyHighContrastModeCssClasses` method is called in the constructor of the `A11yModule` and `MatCommonModule` which means that it'll be invoked whenever a new root injector is created for a module importing any Material module (e.g. lazy-loaded route or dynamically-created component). Since it calls into `getHighContrastMode` and it touches the class list of `document.body`, it has the potential of causing some some slow layouts. This can be observed either when switching pages in the dev app or by profiling the example creation on material.angular.io. These changes resolve the issue by ensuring that we only run the logic once. (cherry picked from commit a92ad3d)
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I noticed this in the profiler while working on angular/material.angular.io#961. The
_applyBodyHighContrastModeCssClassesmethod is called in the constructor of theA11yModuleandMatCommonModulewhich means that it'll be invoked whenever a new root injector is created for a module importing any Material module (e.g. lazy-loaded route or dynamically-created component). Since it calls intogetHighContrastModeand it touches the class list ofdocument.body, it has the potential of causing some some slow layouts. This can be observed either when switching pages in the dev app or by profiling the example creation on material.angular.io.These changes resolve the issue by ensuring that we only run the logic once.