Update Android screen capture implementation

Screen Capture on Android hasn't been updated since it was only exposed
via getUserMedia. This change:
* Adds a UI flag to enable the feature
* Expands the DCHECK to allow getDisplayMedia calls to work
* Removes a DCHECK that width/height are even
  * There was no comment for this DCHECK and if there were a technical
    limitation, it appears to have been removed.

With this change (and the flag enabled) getDisplayMedia seems to work,
at least for a simple golden-path scenario.

Bug: 487935
Change-Id: Ic340345d15798947ba22e9962d5a83a83a974a5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495823
Reviewed-by: Guido Urdaneta <[email protected]>
Commit-Queue: Alexander Cooper <[email protected]>
Cr-Commit-Position: refs/heads/master@{#821402}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9c91757..521a96e 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -4436,6 +4436,10 @@
      kOsAndroid,
      FEATURE_VALUE_TYPE(
          chrome::android::kUpdateNotificationSchedulingIntegration)},
+
+    {"screen-capture-android", flag_descriptions::kUserMediaScreenCapturingName,
+     flag_descriptions::kUserMediaScreenCapturingDescription, kOsAndroid,
+     FEATURE_VALUE_TYPE(chrome::android::kUserMediaScreenCapturing)},
 #endif
 
 #if defined(OS_ANDROID)