Add ThrottleOffscreenAnimatingSvgImages flag to WebView

This is required for running WebView-enabled experiments.

Bug: 1386242
Change-Id: I7dce16ead996033c35853caf54aae32c3fa02c3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4219553
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Auto-Submit: Philip Rogers <pdr@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1100517}

android_webview/java/src/org/chromium/android_webview/common/ProductionSupportedFlagList.java

@@ -320,6 +320,10 @@ private ProductionSupportedFlagList() {}
                             + "using the property tree builder."),
             Flag.baseFeature(BlinkFeatures.THREADED_BODY_LOADER,
                     "If enabled, reads and decodes navigation body data off the main thread."),
+            Flag.baseFeature(BlinkFeatures.THROTTLE_OFFSCREEN_ANIMATING_SVG_IMAGES,
+                    "If enabled, SVG images will suspend animations when all "
+                            + "instances of the image are outside of the "
+                            + "viewport."),
             Flag.baseFeature("PreconnectOnRedirect"),
             Flag.baseFeature("PreconnectInNetworkService"), Flag.baseFeature("PrefetchDNSWithURL"),
             Flag.baseFeature(BlinkFeatures.SEND_MOUSE_EVENTS_DISABLED_FORM_CONTROLS,