[headless] Ensure devtooled tests call Disable/RemoveObserver.

Related to crbug.com/682670, where a missing RemoveObserver() call
caused a segfault. For completeness, this also adds Disable() calls
where they were missing.

BUG=

Review-Url: https://codereview.chromium.org/2642683004
Cr-Commit-Position: refs/heads/master@{#444737}

headless/lib/embedder_mojo_browsertest.cc

@@ -234,14 +234,20 @@ class HttpDisabledByDefaultWhenMojoBindingsUsed : public EmbedderMojoTest,
   }
 
   void ReturnTestResult(const std::string& result) override {
-    FinishAsynchronousTest();
+    DisableClientAndFinishAsynchronousTest();
     FAIL() << "The HTTP page should not have been served and we should not have"
               " recieved a mojo callback!";
   }
 
   void OnLoadingFailed(const network::LoadingFailedParams& params) override {
     // The navigation should fail since HTTP requests are blackholed.
     EXPECT_EQ(params.GetErrorText(), "net::ERR_FILE_NOT_FOUND");
+    DisableClientAndFinishAsynchronousTest();
+  }
+
+  void DisableClientAndFinishAsynchronousTest() {
+    devtools_client_->GetNetwork()->Disable();
+    devtools_client_->GetNetwork()->RemoveObserver(this);
     FinishAsynchronousTest();
   }
 };

headless/lib/headless_devtools_client_browsertest.cc

@@ -65,6 +65,7 @@ class HeadlessDevToolsClientNavigationTest
   }
 
   void OnLoadEventFired(const page::LoadEventFiredParams& params) override {
+    devtools_client_->GetPage()->Disable();
     devtools_client_->GetPage()->GetExperimental()->RemoveObserver(this);
     FinishAsynchronousTest();
   }
@@ -174,6 +175,7 @@ class HeadlessDevToolsClientObserverTest
                                                               &content_type));
     EXPECT_EQ("text/html", content_type);
 
+    devtools_client_->GetNetwork()->Disable();
     devtools_client_->GetNetwork()->RemoveObserver(this);
     FinishAsynchronousTest();
   }
@@ -208,6 +210,9 @@ class HeadlessDevToolsClientExperimentalTest
 
   void OnFrameStoppedLoading(
       const page::FrameStoppedLoadingParams& params) override {
+    devtools_client_->GetPage()->Disable();
+    devtools_client_->GetPage()->GetExperimental()->RemoveObserver(this);
+
     // Check that a non-experimental command which has no return value can be
     // called with a void() callback.
     devtools_client_->GetPage()->Reload(

headless/public/util/dom_tree_extractor_browsertest.cc

@@ -49,6 +49,7 @@ class DomTreeExtractorBrowserTest : public HeadlessAsyncDevTooledBrowserTest,
   }
 
   void OnLoadEventFired(const page::LoadEventFiredParams& params) override {
+    devtools_client_->GetPage()->Disable();
     devtools_client_->GetPage()->RemoveObserver(this);
 
     extractor_.reset(new DomTreeExtractor(devtools_client_.get()));