[fuchsia] Re-enable formerly flaky ContextImplBrowsertests.

The underlying cause of the flakes should be fixed in
crrev.com/98f6ea73.

TBR=wez@chromium.org

Bug: 876894
Change-Id: Ic3549ff80afc6e8041a1195ab71d39b300789e78
Reviewed-on: https://chromium-review.googlesource.com/1187897Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585892}

webrunner/browser/context_impl_browsertest.cc

@@ -148,8 +148,7 @@ IN_PROC_BROWSER_TEST_F(ContextImplTest, NavigateFrame) {
   frame.Unbind();
 }
 
-// TODO(crbug.com/876894): Disabled due to flakiness under QEMU.
-IN_PROC_BROWSER_TEST_F(ContextImplTest, DISABLED_FrameDeletedBeforeContext) {
+IN_PROC_BROWSER_TEST_F(ContextImplTest, FrameDeletedBeforeContext) {
   chromium::web::FramePtr frame = CreateFrame();
 
   // Process the frame creation message.
@@ -519,8 +518,7 @@ struct WebContentsObserverForStop : public content::WebContentsObserver {
   MOCK_METHOD0(NavigationStopped, void());
 };
 
-// TODO(crbug.com/876894): Disabled due to flakiness.
-IN_PROC_BROWSER_TEST_F(ContextImplTest, DISABLED_Stop) {
+IN_PROC_BROWSER_TEST_F(ContextImplTest, Stop) {
   chromium::web::FramePtr frame = CreateFrame();
 
   chromium::web::NavigationControllerPtr controller;