webview: allow DISABLE_GPU_BLOCKLIST in devui.

Allow WebView developers to disable the GPU blocklist via the dev ui for
testing purposes.

Bug: 810928
Change-Id: I4faa0bec2a2c5fa26f84e780f7505ce6e832fab7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404809
Commit-Queue: Richard Coles <torne@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806742}

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

@@ -61,6 +61,9 @@ public final class ProductionSupportedFlagList {
                             + "crash reporting is typically compiled but disabled."),
             Flag.commandLine(GpuSwitches.DISABLE_GPU_RASTERIZATION,
                     "Disables GPU rasterization, i.e. rasterizes on the CPU only."),
+            Flag.commandLine(GpuSwitches.IGNORE_GPU_BLOCKLIST,
+                    "Overrides the built-in software rendering list and enables "
+                            + "GPU acceleration on unsupported device configurations."),
             Flag.baseFeature("OutOfBlinkCors",
                     "Moves CORS logic into the Network Service (rather than inside the blink "
                             + "rendering engine)."),