Remove trailing '\' to avoid build failure on gcc 4.x toolchain.

The trailing '\' on a comment line produces following error on gcc 4.8

chrome/browser/extensions/chrome_url_request_util.h:29:1:
    error: multi-line comment [-Werror=comment]

TBR=fsamuel@chromium.org, lfg@chromium.org, rockot@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/552103003

Cr-Commit-Position: refs/heads/master@{#295278}

chrome/browser/extensions/chrome_url_request_util.h

@@ -26,7 +26,7 @@ class InfoMap;
 namespace chrome_url_request_util {
 
 // Sets allowed=true to allow a chrome-extension:// resource request coming from
-// renderer A to access a resource in an extension running in renderer B.\
+// renderer A to access a resource in an extension running in renderer B.
 // Returns false when it couldn't determine if the resource is allowed or not
 bool AllowCrossRendererResourceLoad(net::URLRequest* request,
                                           bool is_incognito,

extensions/browser/url_request_util.h

@@ -18,7 +18,7 @@ class InfoMap;
 namespace url_request_util {
 
 // Sets allowed=true to allow a chrome-extension:// resource request coming from
-// renderer A to access a resource in an extension running in renderer B.\
+// renderer A to access a resource in an extension running in renderer B.
 // Returns false when it couldn't determine if the resource is allowed or not
 bool AllowCrossRendererResourceLoad(net::URLRequest* request,
                                     bool is_incognito,