Update webrtc.DEPS URL to Git mirror.

Using the Subversion URL will not actually get anything downloaded
anymore (gclient behavior has changed).

Review URL: https://codereview.chromium.org/1017033003

Cr-Commit-Position: refs/heads/master@{#321320}

chrome/browser/media/webrtc_browsertest_common.cc

@@ -32,8 +32,8 @@ static const char kAdviseOnGclientSolution[] =
     "You need to add this solution to your .gclient to run this test:\n"
     "{\n"
     "  \"name\"        : \"webrtc.DEPS\",\n"
-    "  \"url\"         : \"svn://svn.chromium.org/chrome/trunk/deps/"
-    "third_party/webrtc/webrtc.DEPS\",\n"
+    "  \"url\"         : \"https://chromium.googlesource.com/chromium/deps/"
+    "webrtc/webrtc.DEPS\",\n"
     "}";
 
 const int kDefaultPollIntervalMsec = 250;