Create .git-blame-ignore-revs and add Java format CL to it.

.git-blame-ignore-revs

Index: .git-blame-ignore-revs
diff --git a/.git-blame-ignore-revs b/.git-blame-ignore-revs
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+# git hyper-blame master ignore list.
+#
+# This file contains a list of git hashes of revisions to be ignored by git
+# hyper-blame (in depot_tools). These revisions are considered "unimportant" in
+# that they are unlikely to be what you are interested in when blaming.
+#
+# Instructions:
+# - Only large (generally automated) reformatting or renaming CLs should be
+#   added to this list. Do not put things here just because you feel they are
+#   trivial or unimportant. If in doubt, do not put it on this list.
+# - Precede each revision with a comment containing the first line of its log.
+# - Only put full 40-character hashes on this list (not short hashes or any
+#   other revision reference).
+# - Append to the bottom of the file (revisions should be in chronological order
+#   from oldest to newest).
+# - Because you must use a hash, you need to append to this list in a follow-up
+#   CL to the actual reformatting CL that you are trying to ignore.
+
+# Format all Java in WebRTC.
+b6760f9e4442410f2bcb6090b3b89bf709e2fce2