Increase memory size for media_vpx_video_decoder_fuzzer

The maximum frame size in VP8 is 16,384 x 16,384, which uses most of the
default 2048 Mb allowed. Bumping up the size to 4096 Mb to handle the larger
frame size.

BUG=808775
TEST=fuzzer test case passes

Change-Id: I8e1e56bbd0936e745792f34106c7e638ff5a1c2b
Reviewed-on: https://chromium-review.googlesource.com/1100004Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567355}

media/BUILD.gn

@@ -338,7 +338,10 @@ fuzzer_test("media_vpx_video_decoder_fuzzer") {
     ":media",
     "//base",
   ]
-  libfuzzer_options = [ "max_len = 400000" ]
+  libfuzzer_options = [
+    "max_len=400000",
+    "rss_limit_mb=4096",
+  ]
   seed_corpus = "//media/test/data"
 }