Roll chromium_revision 6e6b751..9729297 (334984:335266)

Relevant changes:
* src/third_party/icu: a05f412..00af1a4
* src/tools/gyp: fdcd8bc..5122240
Details: https://chromium.googlesource.com/chromium/src/+/6e6b751..9729297/DEPS

Clang version changed 238013:239765
Details: https://chromium.googlesource.com/chromium/src/+/6e6b751..9729297/tools/clang/scripts/update.sh

TBR=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1199543004

Cr-Commit-Position: refs/heads/master@{#9477}
diff --git a/DEPS b/DEPS
index 6e8bee7..99b48af 100644
--- a/DEPS
+++ b/DEPS
@@ -6,7 +6,7 @@
 vars = {
   'extra_gyp_flag': '-Dextra_gyp_flag=0',
   'chromium_git': 'https://chromium.googlesource.com',
-  'chromium_revision': '6e6b751edaef93725d8ecd8142c32704bfe422e7',
+  'chromium_revision': '972929725afea658f494efdb2876546322391797',
 }
 
 # NOTE: Prefer revision numbers to tags for svn deps. Use http rather than