aw: add EnableSharedImageForWebview flag to DevTools

As EnableSharedImageForWebview was disabled by default this CL adds it
to WebTools UI.

Bug: 900973, 1058524
Change-Id: Ic8d755c3976c0c7d5153aa00727210d1ee2a7b83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2088341Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746968}

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

@@ -49,6 +49,7 @@ public final class ProductionSupportedFlagList {
             Flag.baseFeature("OutOfBlinkCors",
                     "Moves CORS logic into the Network Service (rather than inside the blink "
                             + "rendering engine)."),
+            Flag.baseFeature("EnableSharedImageForWebview", "Enables shared images for WebView."),
             Flag.baseFeature("VizForWebView", "Enables Viz for WebView."),
             Flag.baseFeature("WebViewConnectionlessSafeBrowsing",
                     "Uses GooglePlayService's 'connectionless' APIs for Safe Browsing "