fixup! Reland "Migrate ContentHashFetcher to SimpleURLLoader"

Now that [1] is fixed, we do not need to install the URLInterceptor
as the first thing we do when bootstrap'ing ContentVerifierHashTest.

This CL is a follow up of [2]. It reverts some of the flow changed by
[2] now that we can.

[1] https://crrev.com/c/1117822 (Fix for URLLoaderInterceptor with StoragePartition).
[2] https://crrev.com/c/1076947 (Reland "Migrate ContentHashFetcher to SimpleURLLoader").

BUG=844926

Change-Id: I1f4b2651b3f14196c1523109e8ade5f9cdb3ecac
Reviewed-on: https://chromium-review.googlesource.com/1163862Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#581095}

chrome/browser/extensions/content_verifier_hash_fetch_behavior_browsertest.cc

@@ -320,11 +320,6 @@ class ContentVerifierHashTest
   // Installs test extension that is copied from the webstore with actual
   // signatures.
   testing::AssertionResult InstallExtension(ExtensionType type) {
-    // Install the interceptor at the very beginning of the tests' execution
-    // flow, so that it catches all URLLoaderFactory creations.
-    if (!hash_fetching_disabled_ && !InstallInterceptor())
-      return testing::AssertionFailure() << "Failed to install interceptor.";
-
     // This observer will make sure content hash read and computed_hashes.json
     // writing is complete before we proceed.
     VerifierObserver verifier_observer;
@@ -348,8 +343,8 @@ class ContentVerifierHashTest
 
     info_ = std::make_unique<ExtensionInfo>(extension, type);
 
-    // Set up the data needed by the interceptor functor.
-    if (!hash_fetching_disabled_ && !SetUpInterceptorData())
+    // Set up the interceptor functor and data needed by it.
+    if (!hash_fetching_disabled_ && !InstallInterceptor())
       return testing::AssertionFailure() << "Failed to install interceptor.";
 
     return testing::AssertionSuccess();
@@ -361,6 +356,8 @@ class ContentVerifierHashTest
       return false;
     }
 
+    SetUpInterceptorData();
+
     auto interceptor_function =
         [](GURL* fetch_url, base::FilePath* file_path,
            content::URLLoaderInterceptor::RequestParams* params) {